Asphaltenes are known to deposit in both the petroleum recovery and topside refining processes. The asphaltenes are normally in equilibrium under reservoir conditions. As crude oil is produced, that equilibrium may be disrupted by a number of factors including pressure reductions, crude oil chemical composition changes, introduction of miscible gases and liquids, mixing with diluents and other oils, and, during acid stimulation, hot oiling and other oilfield operations. Electrospray ionization preferentially ionizes polar components of a sample matrix without prechromatographic separation, and its coupling with Fourier transform ion cyclotron resonance mass spectrometry makes a powerful analytical tool for the detailed compositional analysis of petroleum-derived materials such as deposit asphaltenes. In this work, we compare two geographically different crude oils to their corresponding asphaltene deposits. Negative- ion electrospray is preferred because of the acidic nature of asphaltenes. We find that the crude oil deposits contain higher aromatic character ( more unsaturated) and are enriched in oxygenated species as well as multiple heteroatom classes compared to their crude oil counterpart. Such a detailed compositional comparison of the deposit asphaltenes to its crude oil counterpart should help to develop more cost- effective methods to control the deposition of asphaltenes and to increase the overall efficiency of the processing fields with asphaltene problems.