A novel integrated oil extraction process that includes hydrothermal pretreatment and oil extraction (HPOE) from whole oilseeds followed by hydrothermal carbonization (HTC) of the extracted seedcake to hydrochar was developed. Five different types of oilseeds including cotton-, flax-, mustard-, canola-, and jatropha seeds were used in the study. The seeds were subjected to hydrothermal pretreatment in the range of temperatures from 120 to 210 degrees C for 30 min. Oils were extracted from the pretreated seeds using n-hexane in a Soxhlet apparatus for 120 min. The crude oil yields from the pretreated seeds at 180 degrees C and 210 degrees C were significantly higher (up to 30 wt%) than those from the respective untreated ground seeds. The seedcake after oil extraction was subjected to HTC at 300 degrees C with the recycled aqueous phase collected from the pretreatment step. The produced hydrochar had higher heating value of 26.5 kJ/g comparable to that of bituminous coal. BET surface area and pore volume analysis showed that the pretreated seeds had larger surface area and pore volume/size than the respective raw seeds, which resulted in better extractability of oil, shorter extraction time, and overall efficiency of HPOE process. Analyses of the crude oil did not show significant signs of degradation after the hydrothermal pretreatment of oilseeds. The study is the first of its kind where integrated oil extraction and hydrochar production from oilseeds have been studied with the objective of minimizing feedstock preparation and maximizing oil extraction and overall energy conversion using environmentally benign hydrothermal processes. (c) 2015 Elsevier Ltd. All rights reserved.