Seven core samples were submitted for source rock evaluation from the Opoutama-1 well, located on the east coast of North Island, NZ. All seven core samples represent gas source beds. Above 8000ft the organic matter is at pre-peak generation and the shales are potential source beds, but below 8000ft the organic matter has attained early peak generation and the shales have generated and expelled some gas. Oil from the Waitangi seep could not have been generated in these beds. Diagenesis levels indicate that these beds have been exposed to higher subsurface temperatures in the past. Therefore, they are in an arrested state of diagenesis under present geothermal conditions.