This work presents results of a rapid emulsified oil (petroleum) removal from water by flocculation followed by flotation in a modified jet (Jameson) cell (MJC). The modification is such that the downcomer was sealed at the bottom (by a concentric blind-end tube) to allow floated particles to enter immediately into the frothy phase after the capture of the oily flocs by the bubbles. Also, a packed bed (crowder) was placed at the upper part of the concentric tube to stabilize the froth and facilitate the rise of the oil floc/bubble aggregates. The work was divided into two parts: a detailed laboratory study (1.3 m(3)/h) and a pilot plant trial in an offshore platform. Parameters studied were flocculation (type and concentration of polymer), oil concentration, oil droplets size distribution and flotation cell design. Results of laboratory studies showed mean separation efficiencies of the order of 80% when used as a conventional jet cell (CJC) with feed emulsions (droplets size of about 20 mu m) ranged between 100 and 400 mg/L petroleum concentration. The oil removal increased up to 85% in the MJC. These studies allowed optimizing the design and process parameters: chemical, physico-chemical and operating. A MJC (5 m(3)/h) was then projected, built and installed in an offshore platform, after the oil extraction-production point. At optimal conditions, in a single flotation stage, discharges varied between 20 and 30 mg/L oil concentration or 81% removal at 24.7 m(3/)h m(2) loading capacity. Because this jet cell operates with a high air hold-up, it presented a very good efficiency (capture of oil droplets by bubbles) at low residence time (high-rate separation) and showed to be simple, compact and easy to operate. It is believed that the MJC has a great potential for treating polluted oily high flow wastewaters, at high separation rate. Results and mechanisms involved are discussed in terms of interfacial phenomena and design factors. (C) 2011 Elsevier By. All rights reserved.