Canada was the first country to commercially produce oil from oil sands.
The landmark operation was the Great Canadian Oil Sands plant at Fort McMurray, Alberta. It opened on September 30, 1967, and began large-scale commercial production from the Athabasca oil sands. The project was developed by Great Canadian Oil Sands with backing from Sun Oil; it later became part of Suncor Energy.
Oil sands contain bitumen, a dense and highly viscous form of petroleum mixed with sand, clay, and water. Unlike conventional crude, bitumen generally must be mined or produced in place, then heated or diluted and upgraded into a synthetic crude oil. The Athabasca deposit was especially important because some of it lies shallow enough for surface mining.
The question asks for a country, not the company that operated the first major plant. It also refers to commercial production rather than earlier experiments, small pilot projects, or natural bitumen use. Russia, the United States, and Venezuela have petroleum resources and heavy-oil deposits, but Canada established the first large-scale oil-sands industry.