[en] Determining the conditions necessary for the H-transition is important not only for scaling this important confinement regime to future machines but also to aid the understanding of H-mode physics with the hope of further exploiting H-mode confinement. We have done systematic scans of I/sub P/, /bar n//sub e/, B/sub T/, and the X-point to divertor plate distance δ, in single-null diverted discharges, to ascertain their influence on the threshold power required for the L-H transition. During each of these scans, the neutral beam power (H/degree/ → D⁺) was increased in a staircase fashion and the power required for the transition was noted. Over the ranges of: 1 < I/sub P/ (MA) < 2, 1 < B/sub T/(T) < 2, 3 < /bar n//sub e/ (10¹⁹ m/sup /minus/3/) < 8, and 1 < δ (cm) < 23, the threshold power scales as /bar n//sub e/B/sub T/, independent of I/sub P/, and is reduced when δ is small. This method also provided an L-mode power scan over the various plasma conditions, in which we looked for changes in the L-mode plasma, particularly in the edge region, that might trigger the H-transition. Over the range of conditions studied, we found that T/sub e/ (r/a = 0.97)/B/sub T/ approached a critical value before each L-H transition. Various theories have been put forth to explain the bifurcation observed at the L-H transition. We show that the prediction of several of these theories are inconsistent with the observations on DIII-D. 16 refs., 2 figs