The first objective of this project is to develop a user-friendly, PC, foam drilling computer model, FOAM, which will accurately predict frictional pressure drops, cuttings lifting velocity, foam quality, and other drilling variables. The model will allow operating and service companies to accurately predict pressures and flow rates required at the surface and downhole to efficiently drill oil and gas wells with foam systems. The second objective of this project is to develop a lightweight drilling fluid that utilizes hollow glass spheres to reduce the density of the fluid and - allow drilling underbalanced in low-pressure reservoirs. Since the resulting fluid will be incompressible, hydraulics calculations are greatly simplified, and expensive air compressors and booster pumps are eliminated. This lightweight fluid will also eliminate corrosion and downhole fire problems encountered with aerated fluids.