This paper analyzes the reforms of the Spanish electoral finance regulatory system during the nineties. We present a number of indexes to measure the impact of the reforms on parties and campaign spending. We also suggest a game theoretical model to explain why the two main parties agreed to support the legal changes in the nineties. A principal outcome of the reforms was to establish an effective limit to campaign expenses. In our view this would have not been feasible in the late seventies or eighties. Then the parties were trapped in a prisoners dilemma in which each party had to spend more in order to prevent other parties from gaining electoral advantage. But in the nineties the main parties, ridden with problems of soaring electoral debts and disgruntled voters, used the reform of political finance as a coordination device to achieve a Pareto efficient equilibrium.