A viscosified miscible enhanced oil recovery fluid includes (a) a hydrocarbon fluid and viscosifying agent, wherein the viscosified fluid is a Newtonian fluid, (b) a hydrocarbon fluid and gelling agent, wherein the viscosified fluid is a power law fluid, (c) a hydrocarbon fluid, a gelling agent, and a rheological additive, wherein the viscosified fluid is a yield power law fluid, or (d) a hydrocarbon fluid, a gelling agent, a rheological additive, and solvent for the rheological additive, wherein the viscosified fluid is a yield power law fluid. The hydrocarbon fluid is preferably weighted with nano-scale weighting agents. The viscosified fluids are prepared and pumped into a subterranean petroliferous formation to recover a majority of the oil, heavy oil, condensate, or gas originally in place. A method for subsequently recovering a substantial fraction of the miscible injectant conventionally or by applying a viscosity breaker and recovering the viscosity-broken miscible injectant conventionally.