Optimal performance of corrosion inhibiting compounds significantly depends on specific range of inhibitor concentration and measurement time. Data on the protection effect of laurus cassia and rosmarinus angustifolius essential oil extracts on plain carbon steel in 0.5 M H2SO4 and HCl electrolyte was researched into by weight loss analysis. The data showed the admixed extracts were highly potent at the concentrations studied with protection effect typically above 95%. The protection effect increased progressively with measurement time at 1% to 2% extracts concentration beyond which (2.5% to 3% concentration) the results were generally constant. The extracts exhibited inhibition performance independent of concentration. Data on standard deviation showed the degree of deviation of protection effect with measurement time and concentration is minimal. The fraction of protection effect data above 90% protection in H2SO4 is 98% and 100% in HCl solution at limit of errors of 3.24% and 0%. Statistical data by analysis of variance shows both inhibitor concentration and measurement time remarkedly altered the protection effect of the extracts with statistical relevance values of 47.17% and 53.02 for concentration and 26.51% and 29.52% in H2SO4 and HCl solution.