In Performance Chemicals, revenues of $137.2 million were down 5 percent from $143.9 million in the fourth quarter last year. A negative price/mix of 14 percent was offset by higher volumes of 6 percent and a positive currency impact of 3 percent. Gross margins of 21.3 percent were up 2.9 percentage points versus last year. Operating income for the quarter of $18.0 million grew 14 percent on the prior year. For the full year, revenues were down 12 percent to $561.6 million and operating income decreased 43 percent to $54.5 million.
In Fuel Specialties, revenues of $182.1 million were down 1 percent from $183.3 million a year ago. Volumes were flat, and a negative price/mix of 4 percent was offset by a positive currency impact of 3 percent. Gross margins of 32.9 percent were up 5.1 percentage points on last year. Operating income for the quarter of $32.6 million was up 22 percent on last year. For the full year, revenues were down 5 percent to $695.9 million and operating income declined 10 percent to $109.7 million. Adjusting for the impact of non-recurring Brazil inventory charges in the first half of 2023, operating income grew by 3 percent to $125.1 million.
Revenues in Oilfield Services of $175.4 million for the quarter decreased 4 percent from the $183.5 million in the fourth quarter last year. Gross margins declined by 2.4 percentage points from a year ago to 38.0 percent. Operating income of $18.3 million was down 11 percent from $20.5 million last year. For the full year, revenues were up 16 percent to $691.3 million and operating income increased 88 percent to $78.6 million.
Corporate costs of $24.4 million increased by $7.9 million from last year primarily driven by additional remediation charges for legacy closed operations and acquisition related costs.
The full year effective tax rate was 20.2 percent compared to 28.0 percent in 2022. The adjusted effective tax rate was 23.0 percent compared to 27.0 percent last year. The decrease is primarily a consequence of having operations outside of the U.S., which exposes the Company to foreign currency fluctuations, together with the change in profile of our overseas taxable profits by territory year on year.
For the quarter, cash from operations after capital expenditures was $51.3 million compared to $63.3 million a year ago. For the full year, cash from operations after capital expenditures was $130.2 million compared to $39.6 million in 2022. As of December 31, 2023, Innospec had net cash of $203.7 million compared to net cash of $147.1 million a year ago.
Mr. Williams concluded,
“Our business teams delivered a strong overall result in the quarter and full year. Despite our expectation for continued economic headwinds in the coming quarters, we enter 2024 with optimism. Our growing pipeline of technology-based organic opportunities will continue to advance in parallel with our integration of the QGP acquisition.
Cash generation was again excellent in the quarter, and our debt-free, net cash position remained over $200 million after funding the QGP acquisition. Entering 2024 we continue to have significant flexibility and balance sheet strength for further M&A, dividend growth, and organic investment.”
Use of Non-GAAP Financial Measures
The information presented in this press release includes financial measures that are not calculated or presented in accordance with Generally Accepted Accounting Principles in the United States (GAAP). These non-GAAP financial measures comprise EBITDA, income before income taxes excluding special items, net income excluding special items and related per share amounts together with net cash. EBITDA is net income per our consolidated financial statements adjusted for the exclusion of charges for interest expense, net, income taxes, depreciation, and amortization. Income before income taxes, net income and diluted EPS, excluding special items, per our consolidated financial statements are adjusted for the exclusion of amortization of acquired intangible assets, legacy costs of closed operations, foreign currency exchange (gains)/losses, acquisition related costs and adjustment of income tax provisions. Net cash is cash and cash equivalents less total debt. Reconciliations of these non-GAAP financial measures to their most directly comparable GAAP financial measures are provided herein and in the schedules below. The Company believes that such non-GAAP financial measures provide useful information to investors and may assist them in evaluating the Company’s underlying performance and identifying operating trends. In addition, these non-GAAP measures address questions the Company routinely receives from analysts and investors and the Company has determined that it is appropriate to make this data available to all investors. While the Company believes that such measures are useful in evaluating the Company’s performance, investors should not consider them to be a substitute for financial measures prepared in accordance with GAAP. Also, these non-GAAP financial measures may differ from similarly titled non-GAAP financial measures used by other companies and