Steam assisted gravity drainage (SAGD) is the established method for in situ bitumen extraction. However, natural gas powered generation of steam for the SAGD process results in large economic and environmental costs. Alcohol- and alkaline-based additives are emerging strategies to improve SAGD performance, and micromodels are uniquely well-suited to directly compare and quantify the effectiveness of additives with all other variables tightly controlled. The distinct effects of alcohol- and alkaline-based additives on the pore-scale mechanisms were quantified here using a representative high-pressure high-temperature glass micromodel with both optical and thermal imagings (P=0.7 and 1.3 MPa; T=180 and 200 °C). Alcohol addition resulted in viscous fingering, some solvency, oil-wet trapping in the mobile zone, mainly water-in-oil emulsions, and moderate increases in production. In contrast, alkaline addition resulted in water-wet surface condition, emulsification of the bitumen into discrete oil-in-water droplets, and significantly increased production. Temperature profile data combined with optical results were also used to accurately determine the interface and expansion of discrete regions formed during the SAGD including steam chamber, hot water flow zone, mobile zone, and untouched bitumen zone. Alcohol provided only a slight improvement on the steam chamber growth, while alkaline additive expanded the steam chamber by over 10% and significantly improved the overall recovery.