In the Mackenzie–Beaufort region, maximum permafrost thickness is 750 m in the Pleistocene Tuktoyaktuk Coastlands, less than 100 m in the Holocene Mackenzie Delta, and 500 m and anomalously warm in the Big Lake Delta Plain between the two areas. Numerical modelling has been used to derive surface temperature histories that fit ground temperatures and permafrost conditions at 12 wells in the Unipkat, Kumak, and Taglu hydrocarbon fields. The models indicate that the present Holocene Mackenzie Delta was built by fluvial processes into a submarine trough. The delta front passed a site presently some 20 km from the coast about 4.5 ka, and subsequently 58 m of ice-bonded permafrost has aggraded. In contrast, the Big Lake Delta Plain was a subaerial platform for much of the Wisconsinan. It experienced several thousand years of inundation in the Holocene, probably due to widespread development of thermokarst lakes. At sites 8–12 km from the coast, the present subaerial conditions were established 0.5–1.5 ka through lake drainage and fluvial–deltaic deposition.