A town close to Gatwick airport has inched closer to becoming England’s version of Dallas after test results showed an exploration well could contain almost 20m barrels of oil.

In contrast to the gleaming corporate headquarters, cattle herders and endless prairies in the opening credits of the fabled TV soap, the oil find is in woodland at Horse Hill, on the border of Surrey and Sussex. The nearest commercial centre is the commuter town of Horley with its two business parks, modern leisure centre and bustling hospitality industry.

UK Oil & Gas Investments, one of the investors in Horse Hill Developments, the well operator, said preliminary estimates showed there were 3.1m barrels of oil in the well’s upper Portland sandstone, with potential for a further 16.8m barrels nearby. There could also be gas lower down, and the developer expects to drill to that point in the next two weeks.

David Lenigas, UK Oil & Gas’s chairman, who also chairs Horse Hill Developments, said: “We are very pleased with the results so far from this well. The presence of a larger, unappraised, Portland feature creates considerable further upside. We are now looking forward to drilling the Triassic, which is a new and untested exploration target in the area, which, if successful, may contain appreciable volumes of gas.”

However, investors were disappointed with the results, which promised less oil than had been hoped for. UK Oil & Gas shares fell 25% to 1.18p in Friday morning trading. All the other publicly traded investors in the site fell heavily.

Angus Energy, which is not listed on the stock market, owns 40% of Horse Hill Developments. UK Oil & Gas owns 20%, with the remainder shared between Stellar Resources, Solo Oil, Doriemus, Alba Mineral Resources and Regency Mines.

Like JR, the former deal-making eldest Ewing brother in Dallas, Lenigas has faced opposition from environmental campaigners. Protesters from Frack Free Surrey have accused the developers of plotting to use the hotly debated technique to get to the gas. Two women were reported to have chained their arms together to block the entrance to the site.

Horse Hill Developments has said it wants to drill for oil using conventional means and that it has no plans to use fracking.