Using a technique based on holographic interferometry, the total energy transferred from a spark to the surrounding gases was measured for a number of spark plug electrode geometries, flow velocities, gas pressures and coil charge times. A standard automotive ignition coil was used. For the combinations of parameter values studied, we observed ＇＇spark efficiencies＇＇ (ratio of the energy in the gas heated by the spark to the electrical energy supplied to the spark plug) of from 20 to 60 percent. For realistic engine conditions we estimate the quantity of energy transferred to the gas by our ignition system to be roughly 30 mJ. We show how these measurements of total energy transferred to the gas can be used to estimate the spark power vs. time characteristic of a standard inductive ignition system.