The present work focuses on finding the suitability of cotton seed oil as a fuel for diesel engines by comparing the different methods to improve the performance of neat cotton seed oil (CSO). Tests were conducted with neat CSO and diesel to obtain base data. Transesterification with alcohol, preheating of CSO and diesel-CSO blends; blending of orange oil, diesel, or diethyl ether (DEE) with CSO and the use of semi adiabatic engine concept are the methods which have been investigated. The brake thermal efficiency of diesel and neat CSO at peak power is 32.3% and 28% respectively. An increase in the brake thermal efficiency to 30.4% is noticed at peak output with ethyl ester of cotton seed oil (EECSO). Smoke, CO and HC levels are reduced with EECSO compared to neat CSO. A blend of 60% CSO and 40% of diesel results in good brake thermal efficiency and a significant reduction in smoke level. The preheated blend of 60% of CSO and 40% of diesel at 90 degrees C shows an increase in brake thermal efficiency, which is close to diesel. Engine performance improves with the addition of orange oil (OO) and DEE with CSO. The brake thermal efficiency increases with adiabatic engine at part loads compared to neat CSO operation. It is concluded that CSO and EECSO can be directly used in diesel engines without any modifications. However, preheating of CSO or its blend with diesel is a very effective way to lower its viscosity and improve its performance. Blending small quantities of orange oil and diethyl ether with CSO are also other effective methods to improve the performance of diesel engines. (C) 2012 Elsevier Ltd. All rights reserved.