Re: seismic show oil and gas?
There are ways to detect oil and/or gas using seismic. These are called Direct Hydrocarbon Indicators (DHI). Thes form due to the hydrocarbons causing an impedence contrast with neighbouring layers and may indicate the presence of oil or gas. Flatspots and brightspots are the most common examples. Another common technique which specialised processing of raw seismic data allows one to investigate Amplitude Versus Offset (AVO) and can also help one to find hydrocarbons through seismics.
If you do a google search on those keywords you are bound to find some more specific information.