Direct oxygen concentration analysis is gaining importance. In the past, oxygen concentrations were often determined indirectly, by subtracting from 100 the sum of C, H, N, and S concentrations (e.g. ASTM D3176). However, the accuracy of indirect oxygen determination via calculation suffers from the cumulative errors inherent in the analytical methods used for each of the other elements. In addition, it is dependent on the ash content which is obtained, thus introducing another source of error into the indirect oxygen determination. Accurate, unbiased determination of oxygen concentration is therefore only possible through direct measurement. In the fuel industry, as well as in other markets, regulations (cf., ASTM D5622) require precise direct determination of oxygen concentrations. The rapid OXY cube® with its patented backflush technology perfectly fits to these analytical demands with its unrivaled precision.