The purpose of the current study was to determine if the NE system proposed in the NRC, 2012 can be an effective replacement for the ME system. The overall plan was to evaluate the NE system in different situations when diverse rations are formulated. We conducted two experiments: In the first one, we placed 2,054 pigs in a commercial setting from 40 kg to market weight (130kg). Pigs were tested for growth and carcass data. Diets included a simple corn soy diet, diets with corn DDGS, and diets with DDGS+Corn Germ Meal (CGm). These diets were formulated to a constant NE content or a constant ME content. The second experiment, which looked at how the pig utilizes nutrient in the diet involved collection fecal and urine samples from  40 gilts during the growing (39-70kg BW) and the finishing period (70-110kg BW). Digestibility of gross energy (GE) and nitrogen utilization were measured in diets with an increasing amount of each of corn DDGS, CGm, and wheat middlings (0, 12, or 12% inclusion in combination for a total of 0, 18 or 36% co-products). Diets with co-products were fixed to a constant NE content relative to the corn-soy diet by adding fat at 1.6 or 3.3% respectively, or were allowed to decline (no fat added). Results showed that the addition of co-products did not have a negative impact in growth performance when diets are formulated to a constant ME or NE. However some carcass characteristics were impaired when co-products were added at 40%. This seems to have the least impact on the constant NE compared to the constant ME diets. Digestibility of GE decreased when co products were added to the diet, and the inclusion of fat (1.6 and 3.3%) did not help to improve digestibility. Performance in pigs declined with the addition of co-products to the diet using either energy system.  However, the decline was smallest when the diets were formulated using the NE system.  The effectiveness of any energy system will be dependent on our ability to generate accurate energy values on ingredients and on diets.  While the NE system showed advantages over the ME system, neither system was shown to be completely satisfactory in predicting animal performance.