A method of characterizing formation fluid present in a subsurface earth formation during drilling using methods for correcting the measured concentrations of gas components in drilling mud. Gas trap values for the gas components of interest, light hydrocarbons, are measured during mud logging and are corrected using relative response factors, determined from laboratory fluid analysis values and relative extraction efficiency values. The relative response factors for each gas component of interest can be used for correcting additional gas trap values measured in the same well or for correcting gas trap values measured in surrounding wells utilizing a similar drilling fluid. The corrected gas trap values for each of the gas components of interest can be utilized to calculate gas/oil ratios for characterizing the formation fluid from the volume of drilling mud.