This paper investigated the Spanish retail diesel market for evidence of asymmetric price adjustment and rent-seeking following changes in crude oil prices. The study used the nonlinear autoregressive distributed Lag (NARDL) modeling framework and monthly time series data for the period January 2005 to December 2015. The results indicate that Spanish diesel market is fraught with sluggish speed of adjustment, which is typical of markets witnessing uncompetitive pricing and other irregular behaviours by retail firms. The results further indicate that Spanish diesel market is bedeviled by the problem of short-run asymmetric price transmission from crude oil markets, which is consistent with the rockets and fathers effect. Further still, we find that retail firms in the Spanish automotive diesel markets may be exploiting the tax system to conceal rentseeking behaviours. This paper therefore supports policies that will encourage continuous monitoring of the market for irregular behaviors since the observed problems have antitrust and consumer welfare implications.