Mr Obama could be the first black candidate from a major political party
Barack Obama has chosen a high-profile team to help select his running mate, after declaring himself the Democratic nominee for US president.
After the Democratic primaries Mr Obama has enough delegates to be nominated.
His rival, Hillary Clinton, has yet to concede, but there are unconfirmed reports that she will formally announce on Friday that she is dropping out.
Mr Obama would be the first black presidential candidate from a major political party.
Reports, carried by ABC News, that Mrs Clinton was ready to concede came after a conference call to senior Democrats in Congress.
She is planning to hold an event on Friday at which "she will concede the race, once and for all", the US channel reported.
The BBC's Jane O'Brien in Washington says that as Mr Obama was claiming victory, Hillary Clinton stunned even her own supporters with a speech that offered no indication that she was giving up.
There is speculation that the delay was an attempt to position herself as a possible vice-president, our correspondent adds.
Mr Obama's three-member panel comprises Caroline Kennedy, daughter of President John Kennedy, former deputy Attorney General Eric Holder and Jim Johnson.
Mr Johnson performed the same selection task for John Kerry in 2004.
"Senator Obama is pleased to have three talented and dedicated individuals managing this rigorous process," said Bill Burton, a spokesman for the Illinois senator.
"He will work closely with them in the coming weeks but ultimately this will be his decision and his alone."
Earlier, Mr Obama had paid tribute to Mrs Clinton and hinted that she would play a role in any future Obama administration.
Mrs Clinton has said she would be "open" to the idea of being Mr Obama's vice-presidential running-mate.
Referring to a brief conversation he had held with his defeated rival, the Illinois senator said: "I'm very confident of how we're going to be able to bring the party together."
The Republican party's candidate, John McCain has challenged Mr Obama to take part in debates in 10 town hall meetings before August's Democratic convention, and the Obama team is said to be considering the invitation.
The final primaries of the season were held on Tuesday - with Mr Obama winning Montana and Mrs Clinton winning South Dakota.
A candidate needs 2,118 delegates to secure the nomination and Mr Obama now has the support of 2,154 delegates. Mrs Clinton has 1,919.