The efficiency wage model (EWM) has been advanced as an explanation for large and persistent wage differentials. The shirking version of the EWM assumes a trade-off between self-supervision and external supervision. The turnover version assumes turnover is costly to the firm. Variation across firms in the cost of monitoring/shirking or turnover then is hypothesized to account for wage variations across firms for homogeneous workers. Using a new sample of firm data, this paper presents empirical evidence of the trade-off of wage premiums for supervisory intensity and turnover. Little evidence is found to support either version of the EWM.