Abstract Source reconciliation is a procedure for determining the source composition of complex hydrocarbon mixtures such as occur in the atmosphere. Source profiles were determined for the major sources of atmospheric hydrocarbons in the Los Angeles area including automotive exhaust, gasoline, commercial natural gas and geogenic natural gas. Atmospheric hydrocarbon profiles were determined at three sites during the summer of 1973. Multivariate regression analysis was used to determine the optimum source configuration for each atmospheric sample. By this method, the average distribution of nonmethane hydrocarbon emissions from the major sources was found to be: automotive exhaust 47%; gasoline, 31%; commercial natural gas, 8%; and geogenic natural gas, 14%.