The present study aims to explore the performance, emission and combustion characteristics of CI engine fuelled with gutter oil/waste cooking oil obtained from vegetarian and non-vegetarian restaurant used for frying french fries ( WCO1) and chicken ( WCO2) respectively. The engine used for testing is single cylinder CI engine producing 4.4 kW at a constant speed of 1500 rpm. The oils thus obtained are filtered twice to remove any food and other sediments. The waste cooking oil obtained from frying meat have high acidic content, which makes it challenging to convert to biodiesel via transesterification. Hence, Geraniol higher alcohol which is also an acid neutralizer is blended 20% by volume with WCO1 and WCO2 and tested in a CI engine. The experimental results show that brake thermal efficiency (BTE) for WCO1 (29.3%) and WCO2 (28.2%) is less compared to diesel (30.9%). BTE improves with geraniol blending in par with diesel. Geraniol aided in the simultaneous reduction of NO and smoke emission at all the loading conditions. It is evident from the experimental results that WCO with high acid content WCO2) can also be used in CI engine and its performance is improved with geraniol blending. (C) 2018 Elsevier Ltd. All rights reserved.