The laboratory methodology for determining critical gas saturation, S-gc, in field depletion processes is still uncertain. Through measurements on low-permeability rocks, we explore some of the key issues affecting laboratory determination of S-gc. Differences between laboratory depletion and external gasdrive experiments are measured and analyzed. We also investigate the relationship between average S-gc from material balance and true S-gc, source of supersaturation, gas nucleation conditions, and dynamics of gas bubble growth in depletion drive experiments. We assess the use of low-bubblepoint oils to reduce experiment time. Finally, we suggest some improvements to laboratory procedures.