A process for in situ production of shale oil comprises fracturing the target zone 10 of an shale oil formation using a two step approach. First, an initial set of fractures 18 is developed in the formation by using high pressure gas pulses. Second, a secondary set of fractures 28 extending and further fracturing the initial set of fractures 18 is created using a modified ANFO mix 22 wherein rubber particles acting as solid fuel are blended in with ammonium nitrate and fuel oil. The solid fuel enhances the fracturing characteristics of ANFO while minimizing its crushing and compacting tendencies. Hot high pour point oil is then injected into the formation and forced into the receptor well 16 where it is pumped to the surface. By circulating oil in the formation at carefully controlled temperatures, kerogen can be decomposed at the optimum rate to maximize the amount of oil recovered and yield high quality shale oil. High pour point oil reaching cooler extremities of the fractured formation will solidify creating an impermeable perimeter barrier 34 around the target zone 10.