Abstract: Provided herein is a novel method for generating TBP-distillation curves for crude petroleum oils, which curves are free of the large discontinuity in the raw data that is commonly observed when vacuum distillation is begun. The temperature-incremental volume data is accumulated up to a temperature equivalent to about 650.degree. F. at 760 mm. to provide a data bank. The data bank is then used to compute expected yield-temperature values up to a temperature equivalent of 850.degree. F. at 760 mm. The atmospheric residuum is then vacuum distilled and actual yield-temperature datum is compared with expected valves to obtain a deviation. The vacuum is then adjusted to reduce the deviation. Provided also is an automated apparatus for generating such curves.