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The northern region of East Java since the Dutch era has been known as a petroleum producing region. The area is dominated by two west-east ridges, namely Rembang Ridge and Kendeng Ridge with Randublatung Deppression located between. Ridges and depression were formed from the folding due to the Australian plate collision against the Asian plate. Gravity surveys are a geophysical method used to detect large subsurface structures. Gravity measurements were recorded at points in the Mojokerto area, and after appropriate corrections to the gravity calculations obtained Bouguer anomaly contour map. Qualitative interpretation of the Bouguer anomaly contour map shows a high anomaly in the north of the study area, ranging from 450 µGal to 100 µGal with west-east direction. A second anomaly occurs near the middle of the study area, with values ranging from 100 µGal to -50 µGal with west-east direction. And in the southernmost part of the study area a gravity low is present, with values ranging from -100 µGal to -400 µGal with west-east direction. Quantitative interpretation was accomplished by making the A-B cross section on the residual anomalies map (Figure 4). From the AB cross section which is trending northwestsoutheast, the results of modelling with software Gravmag Talwani 2D shows there are seven layers. The lowest layer (basement) is an andesite with density 2,78 g/cc. Above it there is a layer of bioclastic limestone with density 2,6 g/cc and sandy limestone layer with a density of 2,58 g/cc. This layer is covered by a layer of quartz sandstone that is permeable with a density of 2,5 g/cc, which on top of it covered by a layer of sandy marl rock with a density of 2,45 g/cc, marl sandstone with density 2,4 g/cc, and alluvium layer with a density of 1,9 g/cc as the top soil. Cross section A-B depicts two synclines on either side of an anticline and two normal faults on the syncline limb. The peak of the anticline, located at a distance of about 15 km southwest from point A, sits at approximately 500 m below the surface. Hydrocarbons were interpreted at a depth of 500 m to 1000 m on quartz sandstone, overlain by sandy marl rock and sandy limestone serving as a cap rock.