Page 22
                                                          EXHIBIT 4
   THE SECURITIES REPRESENTED BY THIS CERTIFICATE, AND THE SECURITIES ISSUED
   UPON EXERCISE HEREOF, MAY NOT BE OFFERED FOR SALE, SOLD OR OTHERWISE
   TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT FILED
   UNDER THE SECURITIES ACT OF 1933 (THE "ACT"), OR PURSUANT TO AN EXEMPTION
   FROM REGISTRATION UNDER THE ACT WHICH SHALL BE ESTABLISHED TO THE
   SATISFACTION OF THE COMPANY.
 
             Void after 3:30 P.M., Denver Time, on                  , 199
                                                    ---------------      --
 
                                             Warrant to Purchase
                                                          Shares
                                             ------------
                                                 of Common Stock
 
 
                   WARRANT TO PURCHASE SHARES OF COMMON STOCK
 
                                       OF
 
                                  RENTECH, INC.
 
   This Is to Certify That, FOR VALUE RECEIVED,
                                                --------------------------
   -------------------------------------------------------------------------
   or registered assigns ("Holder"), is entitled to purchase, subject to the
   provisions of this Warrant, from RENTECH, INC., a Colorado corporation
   ("Company"), at any time not later than 3:30 P.M., Denver time, on
                             , 199   , one year after the date of this
   --------------------------     ---
   Warrant, (the "Expiration Date")                             shares of
   common stock, having $.01 par value per share, of the Company ("Common
   Stock") at an exercise price, subject to adjustment as set forth below,
   of $0.25 per share.  The number of shares of Common Stock to be received
   upon the exercise of this Warrant and the price to be paid for a share of
   Common Stock are subject to adjustment from time to time as hereinafter
   set forth. The shares of the Common Stock deliverable upon such exercise,
   and as adjusted from time to time, are hereinafter sometimes referred to
   as "Warrant Stock" and the exercise price of a share of Common Stock in
   effect at any time and as adjusted from time to time is hereinafter
   sometimes referred to as the "Exercise Price." 
 
      (a)  Exercise of Warrant.  Subject to the provisions of Section (p)
   hereof, this Warrant may be exercised in whole or in part at any time or
   from time to time not later than 3:30 P.M., Denver Time, on
                        , 199   , or if that date falls on a day on which
   -------------------- banking institutions are authorized by law to close,
   then on the next succeeding day which shall not be such a day, by
   presentation and surrender hereof to the Company with the Purchase Form
   annexed hereto duly executed and accompanied by payment of the Exercise
   Price for the number of shares specified in such form, together with all
   federal and state taxes applicable upon such exercise. If this Warrant
   should be exercised in part only, the Company shall, upon surrender of
   this Warrant for cancellation, execute and deliver a new Warrant evi-
   dencing the right of the Holder to purchase the balance of the shares
   purchasable hereunder.  Upon receipt by the Company of this Warrant at
   the office or agency of the Company, in proper form for exercise, the
   Holder shall be deemed to be the holder of record of the shares of Common
   
                                               Page 23
 
   Stock issuable upon such exercise, notwithstanding that the stock trans
   fer books of the Company shall then be closed or that certificates repre-
   senting such securities shall not then be actually delivered to the
   Holder.  The Exercise Price shall be paid in cash.
 
        (b)  Reservation of Shares.  The Company hereby agrees that at all
   times there shall be reserved for issuance and/or delivery upon exercise
   of this Warrant such number of shares of its Common Stock as shall be
   required for issuance or delivery upon exercise of this Warrant.  
 
        (c)  Fractional Shares.  No fractional shares or scrip representing
   fractional shares shall be issued upon the exercise of this Warrant.
   With respect to any fraction of a share called for upon any exercise
   hereof, the Company shall pay to the Holder an amount in cash equal to
   such fraction multiplied by the current market value of such fractional
   share, determined as follows:  
 
             (1)  If the Common Stock is listed on a national securities
   exchange or admitted to unlisted trading privileges on such exchange, the
   current value shall be the last reported sale price of the Common Stock
   on the composite tape of such exchange on the last trading day prior to
   the date of exercise of this Warrant or if no such sale is made on such
   day, the average closing bid and asked prices for such day on the
   composite tape of such exchange; or 
 
             (2)  If the Common Stock is not so listed or admitted to
   unlisted trading privileges, the current value shall be the mean of the
   last reported bid and asked prices reported by the National Association
   of Securities Dealers Quotation System (or, if not so quoted on NASDAQ,
   by the National Quotation Bureau, Inc.) on the last trading day prior to
   the date of the exercise of this Warrant; or 
 
             (3)  If the Common Stock is not so listed or admitted to
   unlisted trading privileges and bid and asked prices are not so reported,
   the current value shall be an amount, not less than book value, deter
   mined in such reasonable manner as may be prescribed by the Board of
   Directors of the Company, such determination to be final and binding on
   the Holder. 
 
        (d)  Exchange, Assignment or Loss of Warrant.  This Warrant is
   assignable and exchangeable, without expense, at the option of the
   Holder, upon presentation and surrender hereof to the Company or at the
   office of its stock transfer agent, if any, for other Warrants of differ-
   ent denominations entitling the holder thereof to purchase in the aggre-
   gate the same number of shares of Common Stock purchasable hereunder.
   Any such assignment shall be made by surrender of this Warrant to the
   Company or at the office of its stock transfer agent, if any, with the
   Assignment Form annexed hereto duly executed and funds sufficient to pay
   any transfer tax; whereupon the Company shall, without charge, execute
   and deliver a new Warrant in the name of the assignee named in such
   instrument of assignment and this Warrant promptly shall be canceled.
   This Warrant may be divided or combined with other Warrants which carry
   the same rights upon presentation hereof at the office of the Company or
   at the office of its stock transfer agent, if any, together with a
   written notice specifying the names and denominations in which new
   Warrants are to be issued and signed by the Holder hereof.  The term
   "Warrant" as used herein includes any Warrants issued in substitution for
   or replacement of this Warrant, or into which this Warrant may be divided
   or exchanged.  Upon receipt by the Company of evidence satisfactory to it
   of the loss, theft, destruction or mutilation of this Warrant, and (in
   the case of loss, theft or destruction) of reasonably satisfactory
    indemnification including a surety bond, and upon surrender and cancella-

  
                                               Page 24
   tion of this Warrant, if mutilated, the Company will execute and deliver
   a new Warrant of like tenor and date.  Any such new Warrant executed and
   delivered shall constitute an additional contractual obligation on the
   part of the Company, whether or not this Warrant so lost, stolen,
   destroyed, or mutilated shall be at any time enforceable by anyone.
 
        (e)  Rights of the Holder.  The Holder shall not, by virtue hereof,
   be entitled to any rights of a shareholder of the Company, either at law
   or equity, and the rights of the Holder are limited to those expressed in
   this Warrant and are not enforceable against the Company except to the
   extent set forth herein.
 
        (f)  Officer's Certificate.  Upon request by the Holder, and if the
   Exercise Price is adjusted as required by the provisions of Section (f)
   hereof, the Company shall forthwith file in the custody of its Secretary
   or an Assistant Secretary at its principal office, and with its stock
   transfer agent, if any, an officer's certificate showing the adjusted
   Exercise Price determined as herein provided and setting forth in
   reasonable detail the facts requiring such adjustment and the calculation
   thereof.  Each such officer's certificate shall be made available at all
   reasonable times for inspection by the Holder and the Company shall, upon
   request after each such adjustment, mail a copy of such certificate to
   the Holder. 
 
        (g)  Notices to Holders.  So long as this Warrant shall be
   outstanding and unexercised (i) if the Company shall pay any dividend or
   make any distribution upon the Common Stock, or (ii) if the Company shall
   offer to all holders of Common Stock for subscription or purchase by them
   any shares of stock of any class or any other rights, or (iii) if any
   capital reorganization of the Company, reclassification of the capital
   stock of the Company, consolidation or merger of the Company with or into
   another corporation, sale, lease or transfer of all or substantially all
   of the property and assets of the Company to another corporation, or
   voluntary or involuntary dissolution, liquidation or winding up of the
   Company shall be effected, then, in any such case, the Company shall
   cause to be delivered to the Holder, at least 30 days prior to the date
   specified in (x) or (y) below, as the case may be, a notice containing a
   brief description of the proposed action and stating the date on which
   (x) a record is to be taken for the purpose of such dividend, distri-
   bution or rights, or (y) such reclassification, reorganization, consoli-
   dation, merger, conveyance, lease, dissolution, liquidation or winding up
   is to take place and the date, if any, is to be fixed, as of which the
   holders of Common Stock of record shall be entitled to exchange their
   shares of Common Stock for securities or other property deliverable upon
   such reclassification, reorganization, consolidation, merger, conveyance,
   dissolution, liquidation or winding up. 
 
        (h)  Dissolution.  If, at any time prior to the expiration of this
   Warrant and prior to the exercise thereof, any dissolution, liquidation
   or winding up of the Company shall be proposed, the Company shall cause
   at least 30 days' notice to be mailed by certified mail to the registered
   Holder of this Warrant Certificate at his address as it appears on the
   books of the Company.  Such notice shall specify the date as of which
   holders of record of Common Stock shall participate in any distribution
   or shall be entitled to exchange their Common Stock for securities or
   other property, deliverable upon such dissolution, liquidation or winding
   up, as the case may be; to the end that, during such period of 30 days,
   the holders of this Warrant may exercise this Warrant and purchase Common
   Stock (or other stock substituted therefor as hereinbefore provided) and
   be entitled in respect of shares so purchased to all of the rights of the
   other holders of Common Stock of the Company.  In case of a dissolution,
   liquidation or winding up of the Company, all purchase rights under this
   Warrant shall terminate at the close of business on the date as of which
   
                                               Page 25
   holders of record of the Common Stock shall be entitled to participate in
   a distribution of the assets of the Company in connection with such
   dissolution, liquidation or winding up (provided that in no event shall
   said date be less than 30 days after completion of service by certified
   mail of notice as aforesaid).  Any Warrant not exercised prior to such
   time shall be void and no rights shall exist thereunder.  In any such
   case of termination of purchase rights, a statement thereof shall be
   included in the notice provided for herein. 
 
        (i)  Spin-Offs.  In the event the Company spins-off a subsidiary or
   stock held in another corporation as an investment by distributing to the
   shareholders of the Company, as a dividend or otherwise, the stock of the
   subsidiary or other corporation, the Company shall reserve, for the life
   of the Warrant, shares of the subsidiary or other corporation to be
   delivered to the holders of the Warrants upon exercise to the same extent
   as if they were owners of record of the Warrant Stock on the record date
   for payment of the shares of the subsidiary or other corporation.  
 
        (j)  Registration Rights.
 
             (1)  Automatic Registration Rights.  If the Company files a
   registration statement with the Securities and Exchange Commission for
   the Common Stock acquired by the holders of its Nonsubordinated 10%
   Convertible Promissory Notes ("Notes") through exercise of the Notes,
   under conditions provided by the terms of the Notes, the Company shall
   include in the registration statement, and one time only, use its best
   efforts to cause to be registered under the Securities Act of 1933, as
   amended, all of the Common Stock of such holders that they have acquired
   by exercise of their warrants.  The Company will include in the
   registration process only such shares of Common Stock as have been
   acquired by exercise of the Warrants no later than twenty (20) days after
   mailing the Company's notice of its intent to file a registration
   statement to the holders of the Notes.  The Company will file only one
   registration statement for holders of Common Stock acquired upon
   conversion of the Notes and exercise of the Warrants. 
 
             (2)  Piggy-Back Registration.  Subject to Section (k)(7)(D)
   below, if at any time the Company proposes to register any of its Common
   Stock under the Act in connection with the public offering of such
   securities solely for cash on a form that would also permit the
   registration of the Common Stock of the holders that they acquire through
   conversion of the Notes and warrants, the Company shall, each such time,
   promptly give each Holder written notice of such determination.  Upon the
   written request of any Holder given within twenty (20) days after mailing
   of any such notice by the Company, the Company shall use its best efforts
   to cause to be registered under the Act all of such Common Stock so
   acquired that each such Holder has requested to be registered.
 
             (3)  Obligations of the Company.  Whenever required to use its
   best efforts to effect the registration of any Common Stock, the Company
   shall, as expeditiously as reasonably possible:
 
                    (A)  Prepare and file with the Securities and Exchange
   Commission ("SEC") a registration statement with respect to such Warrant
   Stock and use its best efforts to cause such registration statement to
   become and remain effective; provided, however, that in connection with
   any proposed registration intended to permit an offering of any
   securities from time to time (i.e., a so-called "shelf registration"),
   the Company shall in no event be obligated to cause any such registration
   to remain effective for more than one year. 
 
 
 
   
                                               Page 26
                  (B)  Prepare and file with the SEC such amendments and
   supplements to such registration statement and the prospectus used in
   connection with such registration statement as may be necessary to comply
   with the provisions of the Act with respect to the disposition of all
   securities covered by such registration statement. 
 
                  (C)  Furnish to the Holders such numbers of copies of a
   prospectus, including a preliminary prospectus, in conformity with the
   requirements of the Act, and such other documents as they may reasonably
   request in order to facilitate the disposition of Warrant Stock owned by
   them. 
 
                  (D)  Use its best efforts to register and qualify the
   securities covered by such registration statement under such other
   securities or blue-sky laws of such jurisdictions as shall be reasonably
   appropriate for the distribution of the securities covered by the
   registration statement, provided that the Company shall not be required
   in connection therewith or as a condition thereto to qualify to do
   business or to file a general consent to service of process in any such
   states or jurisdictions, and further provided that (anything in this
   Section (k) to the contrary notwithstanding with respect to the bearing
   of expenses) if any jurisdiction in which the securities shall be
   qualified shall require that expenses incurred in connection with the
   qualification of the securities in that jurisdiction be borne by selling
   shareholders pro rata, to the extent required by such jurisdiction.
 
             (4)  Furnish Information.  It shall be a condition precedent to
   the obligations of the Company to take any action that the Holders shall
   furnish to the Company such information regarding them, the Warrant Stock
   held by them, and the intended method of disposition of such securities
   as the Company shall reasonably request and as shall be required in
   connection with the action to be taken by the Company.
 
             (5)  Company Registration Expenses.  In the case of any
   registration effected pursuant to Section (k)(1), the Company shall bear
   any additional registration and qualification fees and expenses
   (excluding underwriters' discounts, commissions and expenses), and any
   additional costs and disbursements of counsel for the Company that result
   from the inclusion of securities held by the Holders in such
   registration; provided, however, that if any such cost or expense is
   attributable solely to one selling Holder and does not constitute a
   normal cost or expense of such a registration, such cost or expense shall
   be paid by that selling Holder.  In addition, each selling Holder shall
   bear the fees and costs of its own counsel.
 
             (6)  Delay of Registration.  No Holder shall have any right to
   take any action to restrain, enjoin, or otherwise delay any registration
   as the result of any controversy that might arise with respect to the
   interpretation or implementation of this Section (l).
 
             (7)  Indemnification.  In the event any Common Stock is
   included in a registration statement:
  
                  (A)  To the extent permitted by law, the Company will
   indemnify and hold harmless each Holder requesting or joining in a
   registration, any underwriter (as defined in the Act) for it, and each
   such person, if any, who controls such Holder or underwriter within the
   meaning of the Act, against any losses, claims, damages, or liabilities,
   joint or several, to which they may become subject under the Act or
   otherwise, insofar as such losses, claims, damages, or liabilities (or
   actions in respect thereof) arise out of or are based on any untrue or
   alleged untrue statement of any material fact contained in such
   registration statement, including any preliminary prospectus or final
   
                                               Page 27
   prospectus contained therein or any amendments or supplements thereto, or
   arise out of or are based upon the omission or alleged omission to state
   therein a material fact required to be stated therein, or necessary to
   make the statements therein not misleading; and will reimburse each such
   Holder, such underwriter, or controlling person for any legal or other
   expenses reasonably incurred by them in connection with investigating or
   defending any such loss, claim, damage, liability, or action; provided,
   however, that the indemnity agreement contained in this Section (k)(6)(A)
   shall not apply to amounts paid in settlement of any such loss, claim,
   damage, liability, or action if such settlement is effected without the
   consent of the Company (which consent shall not be unreasonably withheld)
   nor shall the Company be liable in any such case for any such loss,
   claim, damage, liability, or action to the extent that it arises out of
   or is based upon an untrue statement or alleged untrue statement or
   omission or alleged omission made in connection with such registration
   statement, preliminary prospectus, final prospectus, or amendments or
   supplements thereto, in reliance upon and in conformity with written
   information furnished expressly for use in connection with such
   registration by any such Holder, underwriter, or controlling person.
 
                  (B)  To the extent permitted by law, each Holder
   requesting or joining in a registration will indemnify and hold harmless
   the Company, each of its directors, each of its officers who have signed
   the registration statement, each person, if any, who controls the Company
   within the meaning of the Act, and each agent and any underwriter for the
   Company (within the meaning of the Act) against any losses, claims,
   damages, or liabilities to which the Company or any such director,
   officer, controlling person, agent, or underwriter may become subject,
   under the Act or otherwise, insofar as such losses, claims, damages, or
   liabilities (or actions in respect thereto) arise out of or are based
   upon any untrue statement or alleged untrue statement of any material
   fact contained in such registration statement, including any preliminary
   prospectus or final prospectus contained therein or any amendments or
   supplements thereto, or arise out of or are based upon the omission or
   alleged omission to state therein a material fact required to be stated
   therein or necessary to make the statements therein not misleading, in
   each case to the extent, but only to the extent, that such untrue
   statement or alleged untrue statement or omission or alleged omission was
   made in such registration statement, preliminary or final prospectus, or
   amendments or supplements thereto, in reliance upon and in conformity
   with written information furnished by such Holder expressly for use in
   connection with such registration; and each such Holder will reimburse
   any legal or other expenses reasonably incurred by the Company or any
   such director, officer, controlling person, agent, or underwriter in
   connection with investigating or defending any such loss, claim, damage,
   liability, or action; provided, however, that the indemnity agreement
   contained in this Section(l)(6)(B) shall not apply to amounts paid in
   settlement of any such loss, claim, damage, liability, or action if such
   settlement is effected without the consent of such Holder (which consent
   shall not be unreasonably withheld). 
 
                  (C)  Promptly after receipt by an indemnified party under
   this Section (k)(7) of notice of the commencement of any action, such
   indemnified party will, if a claim in respect thereof is to be made
   against any indemnifying party under this paragraph, notify the
   indemnifying party in writing of the commencement thereof and the
   indemnifying party shall have the right to participate in, and, to the
   extent the indemnifying party so desires, jointly with any other
   indemnifying party similarly noticed, to assume the defense thereof with
   counsel mutually satisfactory to the parties.  The failure to notify an
   indemnifying party promptly of the commencement of any such action, if
   prejudicial to his ability to defend such action, shall relieve such
   indemnifying party of any liability to the indemnified party under this
   
                                               Page 28
   paragraph, but the omission to so notify the indemnifying party will not
   relieve him of any liability that he may have to any indemnified party
   otherwise than under this paragraph.
 
                  (D)  Underwriting Requirements.  In connection with any
   offering involving an underwriting of shares of Common Stock being issued
   by the Company or being sold by persons other than the Holders exercising
   piggy-back registration rights (the "Initial Sellers"), the Company shall
   not be required under Section (k)(2) to include any of the Holders'
   Common Stock acquired by exercise of the Notes and warrants in such
   underwriting unless they accept the terms of the underwriting as agreed
   upon between the Company or the Initial Sellers and the underwriters
   selected by it or them, and then only in such quantity as will not, in
   the written opinion of the underwriters, jeopardize the success of the
   offering by the Company or by the Initial Sellers.  If the total amount
   of securities that all Holders request to be included in such offering
   exceeds the amount of securities that the underwriters reasonably believe
   compatible with the success of the offering, the Company shall only be
   required to include in the offering so many of the securities of the
   selling Holders as the underwriters believe will not jeopardize the
   success of the offering (the securities so included to be apportioned pro
   rata among the selling Holders according to the total amount of
   securities owned by said selling Holders, or in such other proportions as
   shall mutually be agreed to by such selling Holders), provided that no
   such reduction shall be made with respect to any securities offered by
   the Company or the Initial Sellers for its or their own account.
 
             (8)  Termination of the Company's Obligations.  The Company
   shall have no obligations pursuant to this Section (k) more than one (1)
   year after the date of this Agreement.
 
             (9)  Lockup Agreement.  In consideration for the Company
   agreeing to its obligations under this Section(l), each Holder agrees in
   connection with any registration of the Company's securities that, upon
   the request of the Company or the underwriters managing any underwritten
   offering of the Company's securities, not to sell, make any short sale
   of, loan, grant any option for the purchase of, or otherwise dispose of
   any Warrant Stock (other than those included in the registration) without
   the prior written consent of the Company or such underwriters, as the
   case may be, for such period of time (not to exceed 90 days from the
   effective date of such registration) as the Company or the underwriters
   may specify.
 
             (10)  Notice.  Any notices or certificates by the Company to
   the Holder and by the Holder to the Company shall be deemed delivered if
   in writing and delivered personally (including by telex, telecopier,
   telegram or other acknowledged receipt) or three business days following
   deposit in the United States mails, sent by registered or certified mail,
   return receipt requested, addressed as follows:
 
        Holder:
                         ------------------------------
                         ------------------------------
                         ------------------------------
 
        Company:         Rentech, Inc.
                         1331 17th Street, Suite 720
                         Denver, Colorado 80202
                         Attention:  President
 
   Any person may change the address for the giving of notice by notice duly
   given effective five (5) business days thereafter.
 
   
                                               Page 29
        (k)  Amendments and Waivers.  Any term, condition or provision of
   this Warrant may be amended and the observance thereof may be waived
   (either generally or in a particular instance and either retroactively or
   prospectively), with the written consent of the Company and the Holders.
 
        (l)  Entire Agreement.  This Warrant constitutes the entire
   agreement among the parties thereto and supersedes any and all prior
   agreements whether written or oral regarding the subject matter hereof.
 
        (m)  Transfer to Comply with the Securities Act of 1933.
 
             (1)  This Warrant or the Warrant Stock or any other security
   issued or issuable upon exercise of this Warrant may not be offered or
   sold except in conformity with the Securities Act of 1933, as amended,
   and then only against receipt of an agreement of such person to whom such
   offer of sale is made to comply with the provisions of this Section (p)
   with respect to any resale or other disposition of such securities.
 
             (2)  The Company may cause the following legend to be set forth
   on each certificate representing Warrant Stock or any other security
   issued or issuable upon exercise of this Warrant not theretofore
   distributed to the public or sold to underwriters for distribution to the
   public pursuant to Section (l) hereof, unless counsel for the Company is
   of the opinion as to any such certificate that such legend is
   unnecessary:
 
             The securities represented by this certificate may not be
             offered for sale, sold or otherwise transferred except pursuant
             to an effective registration statement made under the
             Securities Act of 1933 (the "Act"), or pursuant to an exemption
             from registration under the Act the availability of which is to
             be established to the satisfaction of the Company.
 
        (n)  Applicable Law.  This Warrant shall be governed by, and
   construed in accordance with, the laws of the state of Colorado.
 
 ATTEST:                            RENTECH, INC.
 
 
 -------------------------      By: 
 Ronald C. Butz, Secretary          -----------------------------------
 Ronald C. Butz, Secretary          Dennis E. Yakobson, President
 
 [SEAL]                         Date:
                                      ---------------------------------