A long-standing hypothesis regarding antibiotic resistance assumes that the evolution of resistant genotypes comes at a fitness cost to individuals. This predicts that resistance will disappear from populations when antibiotic stress is removed because susceptible individuals can then outcompete resistant individuals. However, recent studies have shown that low fitness costs and the evolution of fitness compensation cause very low levels of reversion to susceptibility in some situations. This study evaluated the fitness parameters associated with ampicillin resistance in Escherichia coli under optimal, temperature stressed, and nutrient limited conditions by comparing optical density values between resistant and susceptible individuals. Unexpectedly, the ampicillin resistant population grew faster than the susceptible population under optimal and limited nutrient conditions and experienced no fitness cost under temperature stress conditions. Though ampicillin is not used in clinical settings and E. coli may have different fitness parameters for other antibiotics, using ampicillin as a model suggests that reversion to susceptibility may be unlikely under both optimal growing conditions and stressful conditions. This study illustrates the need for greater understanding of each species' fitness parameters for individual antibiotics and the development of antibiotics that have higher fitness costs and low probabilities of compensation evolution.