This Annual Report provides research accomplishments, publications, and presentations resulting from the FY91 research conducted under the following Base Program projects: reservoir assessment and characterization; TORIS research support; three-phase relative permeability; imaging techniques applied to the study of fluids in porous media; development of improved microbial flooding methods; development of improved surfactant flooding methods; development of improved alkaline flooding methods; development of improved mobility- control methods; gas flooding; mobility control and sweep improvement in gas flooding; thermal processes for light oil recovery; thermal processes for heavy oil recovery; thermochemistry and thermophysical properties of organic nitrogen- and diheteroatom- containing compounds; and development of analytical methodology for analysis of heavy crudes.