UK Oil & Gas (UKOG), the company behind the plan to extract oil from the Gatwick area, says oil has flowed to the surface at a faster rate than expected.
They said light sweet oil rose from 900 metres below ground level at a rate of 463 barrels per day at the Horse Hill site.
Some environmental groups say that getting the oil out of the ground could prove tricky and is only possible through fracking, a controversial extraction method for oil and gas.
But UKOG has said that it does not intend to use fracking to extract the oil.
The company says it could produce up to 500 barrels of oil a day.