Steam cogasification characteristics of petroleum coke with three coals of different ranks were investigated on a laboratory fixed-bed reactor to examine the effects of coal ratios and coal ranks on the gasification reactivity, gas yields, and compositions. Results show that the rise of the coal ratio leads to an increase in H-2 yield and content but a decrease in CO yield and content in the producer gas, independently of coal rank. The cogasification reactivity of petroleum coke (PC) with XLT coal and PC with SF coal at the optimum coal contents of 40% and 80% are about 4.5- and 3.5-fold higher than that of PC gasification alone (XLT = Xiaolongtan lignite from Yunnan province, SF = Shenfu bituminous coal from Shaanxi province); meanwhile, H-2 contents in the producer gas increased by 10.55% and 12.24%. The ordering for the cogasification reactivity of PC with different rank coals is as follows: PC/XLT > PC/SF > PC/GP, which is in accord with the chemical forms of catalytic elements present in the three coals (GP = Gaoping anthracite coal from Shanxi province). Obvious synergistic effects are observed during the cogasification of PC with SF coal and PC with XLT coal. The gases from cogasification of PC with different rank coals can be used as feed gas for the synthesis of DME, methanol, hydrocarbon fuel, and producing hydrogen, depending on coal contents and ranks. Under the present experimental conditions, the thermodynamic equilibrium of the water-gas shift reaction is never reached. The cogasification of PC with low rank coal, especially lignite, to enhance the gasification reactivity of PC and the production of hydrogen-rich gas (up to 64.12%) is a feasible and promising technology to utilize PC on a large scale.