HONG KONG (BLOOMBERG) - The on-again, off-again summit between US President Donald Trump and North Korean leader Kim Jong Un now appears increasingly likely to take place - but it is not yet clear what kind of agreement, if any, the two leaders will be able to reach.

North Korea has ruled out the so-called "Libya model" where it loads its nuclear programme onto planes bound for the United States right away, with Mr Kim saying on Thursday (May 31) that the issue should be "solved on a stage-by-stage basis".

Mr Trump insists that the end goal is denuclearisation, but has left the door open to a phased approach. We take a look at the possible results.

KICK THE CAN DOWN THE ROAD

The most likely outcome may be an agreement to keep talking. Such a deal would involve a lofty declaration that both sides seek peace - even a formal treaty - and a commitment to work towards the goal of ridding the Korean peninsula of nuclear weapons.

Under such a deal, North Korea could announce an extended moratorium on nuclear and missile testing in exchange for modest sanctions relief. The US may also want any agreement to explicitly mention shorter-range missiles so as not to jeopardise alliances with Japan and South Korea, both of which are vulnerable to attack.

Mr Kim said late last year that he had obtained the ability to strike the US with a nuclear weapon. Since then he has unilaterally suspended nuclear and missile tests, closed the test site where the country detonated all six of its nuclear devices, and turned his focus to building the economy.

"It is costless for Kim to say I am not going to do nuclear or missiles tests for now because frankly they are a stage in their cycle where they don't need to," said Dr Vipin Narang, an associate professor of political science at the Massachusetts Institute of Technology who focuses on nuclear issues.

DENUCLEARISATION

This is the biggest sticking point between the two sides. While it is probably unrealistic for Mr Trump and Mr Kim to agree on all aspects of denuclearisation at their first meeting, many experts say it is still possible to go meaningfully beyond a kick-the-can-down-the-road accord.

To do so, they would need to emerge with "a clear sense of what the diplomatic pathway is" for achieving complete and verifiable denuclearisation, said senior research scholar Mira Rapp-Hooper at Yale Law School's Paul Tsai China Centre.

That would include a timetable for detailed negotiations on dismantlement, verification, and implementation phases, according to Mr Douglas Paal, vice-president for studies at the Carnegie Endowment for International Peace. North Korea will be angling to hang on to the weapons "as long as possible", he said.

Dr Lisa Collins, a fellow with the Korea chair at the Centre for Strategic and International Studies, said the time horizon could be a decade.

Mr Trump "seems to think it could happen within three months or six months", she said. "Most nuclear weapons experts I talk to say it will take at least 10 years."

NORTH KOREAN CONCESSIONS

A good deal for the US would eliminate or cap production of North Korea's two classes of intercontinental ballistic missiles - the Hwasong 14 and the larger and more developed Hwasong 15 - as well as shorter-range missiles that would be used in an attack on Japan or South Korea.

North Korea could also agree to limit the size of its stockpile of fissile material used for making nuclear weapons. Such a move would need to be accompanied by credible verification measures and assurances that North Korea's Yongbyon nuclear plant had ceased production. The facility also could be slated for eventual dismantlement.

Experts say verification is the key to any lasting deal. An accord with North Korea will hinge on the degree to which Mr Kim would allow inspectors - such as the International Atomic Energy Agency - access to its facilities to verify commitments.

US CONCESSIONS

Mr Trump could offer Mr Kim a number of immediate and tangible incentives to start getting rid of his nuclear weapons. Chief among them is relief from the tightest economic sanctions the US has imposed on North Korea in decades.

Mr Trump could also reduce the number of US troops in South Korea from the 28,500 currently deployed towards 22,000, the minimum allowed under an amendment to the National Defence Authorisation Act passed by Congress and confirmed on May 14. This is something Mr Trump talked about in his election campaign.

In a more modest step, the US could agree to limit the size and scope of its military exercises. North Korea would likely be expected to curtail its military drills in return.

RISKS

The biggest risk for the US is that Mr Trump simply concedes too much in return for too little, limiting leverage for pushing future steps towards denuclearisation.

For instance, North Korea would benefit from an agreement that is drawn out and involves each side making incremental concessions rather than laying out significant actions within a set timetable, Dr Stephan Haggard, distinguished professor at the University of California-San Diego, said in a Lawfare Institute podcast in May.

Past deals have fallen apart due to disputes over inspections and the delivery of promised economic aid. And implementation of any deal is likely to stretch beyond the term of Mr Trump, who can stay in power until January 2025 if he manages to win re-election, while Mr Kim faces no term limits.

Also looming over the talks is the possibility that Chinese and South Korean enthusiasm to engage economically could overwhelm US efforts to drive a hard bargain.

"There's this excitement to engage North Korea, and I'm afraid it'll be very hard to keep them on the same page with us to make sure we don't loosen sanctions before North Korea takes concrete steps," said nuclear security fellow Patricia Kim at the Council on Foreign Relations.

HITTING IT OFF

The two leaders might even bond, which could be more decisive than any written declaration, according to retired army colonel William McKinney, who spent more than 40 years involved in US-Korea military relations and planning.

"If they walk away from the table and feel confident that they know the other person, then what the two of them say in terms of the communique will have some validity," said Mr McKinney. "That is the most important aspect of this summit."

NO DEAL

There is still a risk the meeting never even happens, and if it does, it could simply fall apart.

Mr Trump's mercurial negotiating approach has yet to prove effective in reaching new deals on the global stage - if anything so far he has proven far more adept at cancelling agreements than creating them.

Mr Trump risks being cast as the spoiler if he pushes too hard, said Mr Patrick Cronin, director of the Centre for a New America Security's Asia-Pacific security programme.

"If Trump gets a big piece of the nuclear pie of North Korea and he turns it down, there's a risk that we'll look like we were the stubborn belligerent party, and North Korea was the reasonable party," he said.