Up to 250 jobs are being created at the first deep mines to open in south Wales for three decades.
Hundreds of jobs could be created at the new mines
Unity Mine at Cwmgwrach, in the Neath Valley, is due to begin production within weeks, taking on 60 workers.
Owners of a nearby mine at Aberpergwm say they are close to accessing a large coal reserve, meaning up to 200 more workers will be needed.
Unity chairman Gerwyn Williams said he planned to open more mines in south Wales to meet Europe's "energy gap".
Final preparations at Unity mine are taking place ahead of the beginning of production in June.
Mine owner Unity Power said it plans to increase production to one million tonnes of coal a year.
Currently, the only deep mine operating on the once-thriving south Wales coalfield is Tower Colliery, near Hirwaun, which has been run by its workers since 1995.
Tower is due to close early next year though, because its reserves are exhausted.
Gerwyn Williams said he believed the new pit would be viable
No new deep mine has opened in south Wales since Betws colliery near Ammanford in 1974.
Gerwyn Williams told BBC Wales' Week In Week Out programme he was confident the new mine was viable, adding it could herald the opening of four further pits by his company across south Wales.
He said: "In seven or eight years a lot of things have changed. The price of coal has gone up and Europe is faced with an energy gap.
"We don't think that renewables are going to meet the gap that we've got, so everybody will come back to coal."
Tyrone O'Sullivan, chairman of Tower Colliery, said the possibility of new mines opening was an opportunity to prevent the skills of Wales' miners from being lost.
He said: "If somebody had said to me, when it comes to the end of Tower, there will be a brand new pit, ready to be developed, I would say they were dreaming.
"But that's exactly how it's going to happen, and I think it's an exciting time for Wales."
But Mr Williams, of Unity Power, warned he may have to recruit foreign workers, possibly Polish, because of the lack of miners remaining in Wales.
There have been no deep mines opened in Wales since the 1970s
He said: "I don't know where we are going to get them - we can't just click our fingers.
"There are mining men all over the world that want to come to the UK to work and while we want to employ local people I'm afraid that there is going to be a period where we are going to have to bring in skills from overseas."
As well as Unity mine, a neighbouring pit is preparing to access what is believed to be the biggest reserve of anthracite in Europe.
Energy Build Holdings said it was within 500 metres (1,640ft) of a 9ft (2.7m) seam of coal at Aberpergwm after a decade of development work.
Company spokesman Rhidian Davies said the mine had great potential.
"There's more than enough coal there to keep me in work and many others for 40 to 50 years", he added.
"The potential here is vast, there's many millions of tonnes there."
Week In Week Out is broadcast on BBC One Wales at 2235 BST on Tuesday and on BBC2W at 2030 BST on Thursday.