[en] Understanding and increasing the energy confinement time (/tau//sub E/ /identical to/ W/P) remains a primary goal of fusion research. This objective is being pursued on DIII-D via investigations of /tau//sub E/ in limiter and single- and double-null divertor discharges with Ohmic heating and neutral beam heating. This paper examines the dependence of /tau//sub E/ on ion mass, plasma current, neutral beam power, toroidal field, and safety factor. The data presented is for neutral beam injection in the direction of the plasma current, although /tau//sub E/ is the same for both co- and counter-injection. 12 refs., 5 figs