Embodiments are directed to performing material balance analysis for tanks in a petroleum reservoir and to performing dual porosity material balance analysis. In one scenario, a computer system divides a reservoir into multiple tank blocks, where at least two tank blocks are adjacent. The adjacent tanks are connected at a tank block boundary so that materials are permitted to travel between the tank blocks. The computer system determines flow rate between adjacent tank blocks proportional to the difference in tank block pressures. Then, upon making this determination, the computer system determines material balance for at least some of the tank blocks in the reservoir through influx and efflux of material across the tank block boundary. The material balance includes a determined material balance for one of the adjacent tank blocks and a determined material balance for the other adjacent tank block.