Plans for cutting greenhouse gases, using carbon tax receipts and the age for qualifying for the State pension are among the remaining outstanding issues in government formation talks.
The full negotiating teams from the three parties are set to meet again today as they race against time to agree a programme for government that can be ratified by their memberships by the end of the month.
The three leaders - Taoiseach Leo Varadkar of Fine Gael, Fianna Fail's Micheal Martin and Eamon Ryan of the Green Party - may also meet again today as they seek to thrash out a deal.
However, there are a number of key areas yet to be agreed on by the three parties.
There is agreement in principle on a Green Party demand that carbon emissions should be reduced by 7pc-a-year, but the detail of how to do this is still being discussed.
A Green Party source was optimistic this can be resolved, despite issues on how agriculture and transport will contribute.
Climate Action Minister Richard Bruton last night said 7pc was an "ambitious target" and "we will have to be very imaginative, not just today in framing a programme for government, but over the decades in developing policies that can deliver this".
"It's challenging in these talks and will be challenging as we go along, but it's really important that we get a good understanding between all parties as to how we are going to set about delivering this, and I think these negotiations will set those signposts very clearly," he said.
On the carbon tax, the Green Party has been pushing for a so-called "fee and dividend" approach that would see refunds to households.
Mr Ryan signalled a rowing back from this position in a newspaper interview, in which he proposed ring-fencing of the funds to ensure a "just transition" away from fossil fuels.
A Green Party source said this could involve measures to help alleviate fuel poverty, like retrofitting social housing units rather than refunding the carbon tax directly.
Sources in all three parties said work remained on the pension age.
Fianna Fail wants the rise in the pension age to 67, due to happen next year, to be delayed.
This has been resisted by Fine Gael, which has been insisting on it being increased in line with a long-running strategy aimed at reducing State pension costs - albeit with a transitional payment for people until they reach 67.
Mr Bruton, one of Fine Gael's negotiators, said of the prospect of reaching a deal on government formation this week: "There's been an immense amount of work done.
"I think we have got to the point where we have a good understanding of the different parties' positions and I think it is workable to find solutions."