Petrosys surface modeling has the unique ability of being able to simultaneously model data from multiple input sources, drawing on a range of vendor applications and data stores. Surface models and maps are enhanced by greater access and run time filtering of data, supporting a geoscientist’s ability to evaluate and conclude their interpretation on time.Grids in Petrosys are engineered to handle the wide range of surface modeling challenges in E&P work ranging from the field to the regional scale. Our flexible grid geometry supports very large grids defined in any projected or geographic coordinate reference system. Intelligent interpolation within grid cells allows high resolution output to be generated without the computational overheads of excessively fine grids.Contours help geoscientists visualise and refine interpretation, and are a vital component of reserves maps. Petrosys provides a high standard of contour displays including good matching of fault cuts, optional blanking of contours in areas of steep gradients, and orthocontouring. Graphical re-interpretation of contours and faults can be applied to update either an entire grid or a restricted area such as that affected by a recently drilled well.Gross rock volumes can be easily calculated from top, top and base, or thickness grids with optional user defined scale factors and volume units. Extensive quality assurance procedures ensure consistent and reliable volume estimates.