Oneworld alliance members British Airways (BA), American Airlines (AA) and Iberia are volunteering four daily pairs of slots at Heathrow for other airlines to lease.
In a bid to pave the way for European Commission (EC) approval of the airlines' proposed joint venture on transatlantic routes, the airlines have said they will make available a number of take off and landing slots to non-oneworld alliance airlines.
Under the proposed joint venture, the airlines would share revenues on routes between North America and Europe, as well as co-operate on schedules and pricing.
Slots on the following routes will be up for lease: Heathrow or Gatwick to Boston, Heathrow or Gatwick to Dallas Fort Worth, and Heathrow or Gatwick to Miami.
At some point in the future, Heathrow or Gatwick to New York slots could become available "should today's competitive market change", said BA.
The slots don't need to be currently used on these routes, and the EC has agreed that the airlines should be compensated financially by airlines leasing the slots.
Willie Walsh, British Airways CEO, said: "We've offered to lease slots to gain EC approval for our joint business which will bring benefits to our customers, shareholders and employees. It will also enable oneworld to compete on a level playing field with the other global alliances across the Atlantic.
"We're pleased that the EC has recognised that we should be compensated for leasing the slots. This reflects the fact that there is an active slots market in London where slots are generally traded for value".
The EC will now "seek the views of interested parties on the airlines' proposed commitments", said BA.
Sir Richard Branson, president of rival airline Virgin Atlantic, dismissed the proposed slots package as "woefully inadequate in counter-acting the anti-competitive harm of a combined BA/AA." He said the proposals fall short of what is necessary.
"I continue to question why the Commission is even considering these proposals to try and put right the consumer harm of this monster monopoly when it does not seem to have any evidence of concrete consumer benefits. You can't remedy the irremediable," said Branson.