Selling, general and administrative expenses for the three months ended October 31, 2021 and 2020 were $11.6 million, or 9.3% of corresponding consolidated revenues, and $9.4 million, or 7.4% of corresponding consolidated revenues, respectively.
Due primarily to the increase in consolidated pre-tax book income to $15.7 million for the three months ended October 31, 2021 from $11.1 million for the three months ended October 31, 2020, we reported income tax expense in the amount of $3.3 million for the current period. Income tax expense for the three months ended October 31, 2020 was $1.7 million.
For the three months ended October 31, 2021, our favorable overall operating profit performance resulted in net income attributable to our stockholders in the amount of $12.4 million, or $0.78 per diluted share. For the comparable period last year, we reported net income attributable to our stockholders in the amount of $9.5 million, or $0.60 per dilutive share.
Consolidated revenues for the nine-month period ended October 31, 2021 were $383.8 million; this amount represented a 39.6% improvement from the amount of revenues for the nine months ended October 31, 2020. The revenues of the power industry services segment increased by $68.3 million to $295.7 million for the nine months ended October 31, 2021, from $227.4 million reported for the nine months ended October 31, 2020. The revenues of the power industry services segment represented 77.1% and 82.7% of consolidated revenues for the nine months ended October 31, 2021 and 2020, respectively. The industrial services business reported revenues of $78.2 million for the nine months ended October 31, 2021. This amount represented an increase of $36.0 million, or 85.5%, from revenues of $42.2 million reported by this business for the nine months ended October 31, 2020. Revenues provided by this reportable business segment represented 20.4% and 15.3% of corresponding consolidated revenues for the nine months ended October 31, 2021 and 2020, respectively.
Consolidated gross profit for the nine months ended October 31, 2021 was $77.5 million, or 20.2% of the corresponding consolidated revenues, which reflected primarily the favorable impact of higher consolidated revenues. For the nine months ended October 31, 2020, our consolidated gross profit was $40.0 million, or 14.5% of corresponding consolidated revenues for the period.
Selling, general and administrative expenses were $31.8 million and $28.8 million for the nine months ended October 31, 2021 and 2020, respectively, or 8.3% and 10.5% of revenues for the corresponding periods, respectively.
Due primarily to the consolidated pre-tax book income reported for the nine months ended October 31, 2021 in the amount of $47.3 million, we reported income tax expense in the amount of $11.2 million for the period. For the nine months ended October 31, 2020, we recorded an income tax benefit in the amount of $1.4 million which reflected primarily a net operating loss carryback benefit of $4.4 million, most of which was recorded in the first quarter last year.
For the nine months ended October 31, 2021, our improved overall operating performance resulted in net income attributable to our stockholders in the amount of $36.0 million, or $2.25 per diluted share. For the comparable period last year, we reported net income attributable to our stockholders in the amount of $14.3 million, or $0.91 per dilutive share.
The primary drivers of our strong financial performance for the three and nine months ended October 31, 2021 were the revenues and gross margin contributions associated with the construction projects of GPS. These projects represented the major portion of our business for the periods.
We believe that all of our businesses have been adversely impacted, to some degree, by difficulties presented by the COVID-19 pandemic, especially last year when the outbreak commenced. For example, the results for APC were hurt by the slow resumption of postponed Irish works projects and the suspension and restart of construction activities on a certain major project. The challenges of managing the continuing activities of the Guernsey Power Station project during the periods of various health and safety restrictions have resulted in modifications to construction plans and schedules. In addition, our consolidated revenues for the nine months ended October 31, 2020 in particular suffered from the effects of project delays by customers of both TRC and SMC attributable to the restrictive work environments caused by the pandemic.
We believe that all of our operating companies have managed the challenges presented by this ongoing pandemic with relative success so far. A significant amount of effort has been spent by senior and project management to ensure the safety of our employees during the COVID-19 pandemic while we continued to satisfy our customer obligations. While our pro-