In this paper, a zero-dimensional (0D) single-zone combustion model was applied for predicting combustion and indicated engine parameters in a spark ignition (SI) engine. Three different shale gas mixtures, methane, and liquefied petroleum gas (LPG) (30% C3H8–70% C4H10), were studied as SI engine fuel. The shale gas compositions included shale gas-1 (86% CH4–14% C2H6), shale gas-2 (81% CH4–10% C2H6–9% N2), and shale gas-3 (58% CH4–20% C2H6–2% C3H8–10% CO2). Experimental results of the SI engine operated with LPG were used in the model verification phase and provided to the validation of the theoretical model. In addition, the operational parameters of the LPG engine were used as the model input values. The results show that shale gas-1 has the potential to be a good alternative fuel to LPG for SI engines. Shale gas-1 has an indicated mean effective pressure (IMEP) value of 5.7–7.3%, which is lower than LPG in the range of ϕ = 0.83–1.2. Furthermore, LPG has a 27.7% higher indicated specific fuel consumption (ISFC) compared to shale gas-1. On the other hand, LPG has 1.2–2.4 units lower indicated thermal efficiency (ITE) values than shale gas-1 in the range of ϕ = 0.83–1.2. However, Methane, Shale gas-2, and Shale gas-3 have 7.55–9.62%, 20.35–20%, 22.19–21.47 lower IMEPs than LPG in the range of ϕ = 0.83–1.2, respectively.