This study examined assessment item difficulty patterns in two energy aspects, energy source/form/transfer and energy degradation/conservation, across and within science disciplines. The participant students were taking at least one college-level introductory science course. Findings showed a common pattern of item difficulties for the two energy aspects across science disciplines; energy degradation/conservation items were, in general, more difficult than energy source/form/transfer items. The effects of energy aspects on item difficulty were not found to be significantly different across disciplines. However, item difficulty levels for energy source/form/transfer items varied more than those of energy degradation/conservation items. Further analysis of item difficulties for energy aspects by science content topics within each discipline revealed different sequences of item difficulty between the two energy aspects across science content topics. Together, these findings showed more promising characteristics of energy degradation/conservation than the energy source/form/transfer aspect as a cross-disciplinary energy concept.