A drilling fluid compound, for use as an additive in a water-based drilling mud system, comprises a neat (B100) biodiesel liquid at a concentration of at least 5% by volume, and is useful in downhole applications such as lubrication, spotting, shale inhibition, fluid loss control, and rate of penetration enhancement. A base fluid for a synthetic-based drilling mud system comprises a B100 biodiesel liquid at a concentration of at least 5% by volume. A polyalphaolefin, another isomerized olefin, a petrodiesel, a mineral oil, a mineral oil derivative, or combinations thereof, may also be included in the drilling fluid compound or in the base fluid, within suitable ranges. The compositions of matter satisfy the current environmental standards defined by the U.S. Environmental Protection Agency for drilling fluids.