With the Mangala oil discovery in 2004, Cairn established the Barmer Basin of Rajasthan as a major new hydrocarbon province. Most reserves are contained in fluvial sandstone reservoirs of the Fatehgarh Formation, which probably ranges in age from Late Cretaceous to Early Paleocene. The Fatehgarh sandstones were mainly derived from reworking of Mesozoic sandstones at the northern end of the Barmer rift, but with some volcaniclastic input probably derived from Deccan volcanic rocks within and on the margins of the rift. These thick, quartz-rich, high porosity and permeability sandstones provide an excellent oil reservoir in the north of the Barmer Basin, but the increasing volcanic influence further south causes reservoir quality and thickness of net sand to deteriorate. This paper relates how the tectonic and volcanic evolution of the northwest margin of the Indian plate has influenced the depositional trends which have resulted in formation of this world class reservoir.