Energy firm Cuadrilla has had “very encouraging” early results from its shale gas exploration site in Lancashire, it said.
The company said a pilot well drilled down 2.7km (1.7 miles) at Preston New Road, in Fylde, had been completed and core samples showed the rock was suitable for hydraulic fracturing, or fracking.
Cuadrilla said it was confident there was a “very sizeable quantity of natural gas” in the shale rock formation.
Vertical sections of two exploratory wells have been drilled and work has started on the first of the horizontal wells, with fracking likely to start in the second quarter of this year, it said.
The controversial process involves drilling vertically deep underground and then horizontally, before pumping in liquid at high pressure to fracture shale rock and release gas trapped in the shale.
The site at Preston New Road has been the focus of controversy over the development of a fracking industry in the UK.
It was refused planning permission by Lancashire County Council in 2015, but permission was later granted following an appeal and a planning inquiry.
In April last year, campaign groups lost a High Court action to overturn the decision, but protests continue at the site where Cuadrilla has permission to drill up to four exploratory wells.
Data gathered from the core samples suggests “excellent rock quality for hydraulic fracturing and a high natural gas content in several zones within the shale”, the company said.
Chief executive Francis Egan said: “We are very encouraged by our early analysis of the data and confident that there is a very sizeable quantity of natural gas in the Bowland Shale.
“In addition we can confirm that the rock composition is very suitable to hydraulically fracture.
“This give us great confidence as we start drilling what will be the first horizontal well drilled into UK shale rock.”
Exploration in Lancashire marks part of the efforts by several companies to get the shale industry in the UK off the ground, amid hopes it will boost the economy, jobs and energy security.
But opponents of fracking fear it can cause earthquakes, pollute water, lead to damaging development in the countryside and hit house prices, and is not compatible with targets to cut the use of fossil fuels to tackle climate change.
Greenpeace UK’s Emma Gibson said any shale gas Cuadrilla got out of the ground would be a problem for Britain, not a resource.
“The government’s own figures show that the amount of electricity generated by burning gas is expected to halve by 2025, and by then renewables will have overtaken gas as Britain’s main power source,” she said.
“The UK doesn’t need fracking in its energy future and can’t afford it if we’re to tackle climate change.”
She urged Mrs May to ban fracking and throw her weight behind renewable energy instead.
Rose Dickinson, Friends of the Earth campaigner, said the fracking industry had been producing “little more than hot air” for six and a half years, while renewable energy had increased to provide a third of the UK’s power.
She added: “Fracking makes no sense for our climate, our energy needs, or our economy.
“With opposition continuing to grow locally, and across the country, and the industry being stopped in Scotland, Wales and Northern Ireland, today’s development seems little more than a last gasp of PR spin for an industry in its death throes.”