Elms, who follows the negotiations, said she expected a deal to be finalized in March. Others have predicted similar.
"It's easy to get a quick agreement: you just drop the level of ambition. There was no temptation to do that," U.S. Trade Representative Michael Froman told reporters in a conference call after the talks. He said the 12 countries are focused on reaching a "high-standard" agreement.
Negotiators are aiming to reduce tariffs on goods and services to close to zero. They are also trying to ensure that foreign companies operating in those markets have a level playing field with state-owned ones, and that their products are not counterfeited.
The block includes developing countries with large state-owned industries such as Vietnam and Malaysia as well as rich nations including the United States and Japan.
The agreement would encompass around one-third of world trade and 800 million people. Proponents say it should lead to greater economic growth.
Any deal will have to be ratified by the U.S. Congress, where Democratic lawmakers in particular are calling for tough provisions on environmental and labor standards and against currency manipulation. To simplify ratification, the Obama administration wants Congress first to pass legislation that gives it authority to negotiate trade deals that Congress can accept or reject but cannot change.
Non-governmental organizations have also been seeking to influence the agreement to get a better deal for the poor.
They fear that the cost of medicines may rise in countries such as Vietnam because U.S. pharmaceutical companies are pressing for long periods of patent protection, slowing the release of generic versions of drugs.
The talks in Singapore followed a World Trade Organization summit in Bali last week at which the organization's 159 member economies agreed to cut customs red tape. It was the first WTO deal since the global trade body was formed in 1995.
The countries negotiating the TPP are Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.
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Associated Press writer Matthew Pennington in Washington contributed to this report.