With a production of 208.2 m3/d, heavy oil was produced by drill stem test (DST) from three shallow reservoirs in Sand Group Nos. Ⅰ and Ⅲ of the Neogene Guantao Formation (NgⅠ and NgⅢ) and the Eogene Dongying Formation (Ed) in an exploratory well Ban-14-1 within the Qianmiqiao region, Bohai Bay Basin, northern China. Based on the GC and GC-MS data of the NgⅠ and NgⅢ heavy oil samples, all n-alkanes and most isoprenoid hydrocarbons are lost and the GC baseline appears as an evident "hump", implying a large quantity of unresolved complex mixture (UCM), which typically revealed a result of heavy biodegradation. However, there still is a complete series of C14-C73 n-alkanes in the high-temperature gas chromatograms (HTGC) of the heavy oil, among which, the abundance of C30- n-alkanes are drastically reduced. The C35-C55 high molecular weight (HMW) n-alkanes are at high abundance and show a normal distribution pattern with major peak at C43 and an obvious odd-carbon-number predominance with CPI37-55 and