The hydrocarbon-productive James reef at Fairway field, trending nearly at a right angle to the Lower Cretaceous strandline, has been proven by detailed facies mapping and key well control to have an atoll reef configuration. Facies of the atoll are differentiated into: (I) two northwest trending reefs of algal stromatolite-hydrozoan boundstone (lowermost zone), Chondrodonta wackestone (middle zone), and rudistid boundstone and wackestone (uppermost zone); (2) lenticular bodies of reef-derived skeletal grainstone that flank the reefs; and (3) lagoonal limestones characterized by interbedded miliolid-peloidal grainstone, algal nodule wackestone, and biostromes of rudistid wackestone and Chondrodonta wackestone. The thickest sections of the lagoonal facies lie between the reefs, and the reef facies appear to partially enclose the lagoonal facies. The off-reef facies, which developed contemporaneously with reef growth, consist of argillaceous, skeletal packstone, wackestone, and mudstone.