In this paper three implicit-explicit (IMEX) time semi-discrete methods, namely IMEX-BDF1, IMEX-BDF2 and CN-LF, are developed for solving parabolic partial integro-differential equations which arise in option pricing theory when the underlying asset follows a jump diffusion process. It is shown that IMEX-BDF2 and CN-LF are stable and second order accurate, whereas IMEX-BDF1 is stable but only first order accurate. After time semi-discretization, the resulting linear differential equations are solved by using a cubic B-spline collocation method. The methods so developed have computational complexity of O(MNlog2(M))\documentclass[12pt]{minimal}
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\begin{document}$$O(MNlog_{2}(M))$$\end{document} for Merton model and of O(MN)\documentclass[12pt]{minimal}
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\begin{document}$$O(MN)$$\end{document} for Kou model, where N\documentclass[12pt]{minimal}
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\begin{document}$$N$$\end{document} denotes the number of time steps and M\documentclass[12pt]{minimal}
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\begin{document}$$M$$\end{document} the number of collocation points. Some numerical examples, for pricing European options under Merton and Kou jump-diffusion models with constant as well as variable volatility, are presented to demonstrate the stability, convergence and computational complexity of the methods.