Josh Tenorio, Obama's campaign manager in Guam, told Reuters news agency: "Clearly, both of them are quite popular and we should celebrate that."
Guam's residents cannot vote in the presidential election but the territory, which is less than a fifth of the size of the smallest US state of Rhode Island, sends four pledged delegates and five superdelegates to the Democratic National Convention in August.
The results splits the pledged delegates t between the two candidates.
"We can't vote for president, but this is our part of the process," Robert Lizama, a local mayor, said.
"It's brought a lot of awareness and participation. I think that's important.
'Democrat for a day'
Party officials said many people had registered as Democrats at
the caucus sites around the island, prompting the tag "Democrats for
"There are many new Democrats today," Herbie Perez, the chairman of the Democratic nominating committee, said.
Neither candidate campaigned in Guam in person but did call radio stations to emphasise their affinity with island.
Clinton reminded voters about her multiple visits during stopovers on presidential trips with her husband, and Obama emphasised his Pacific connections through his upbringing in Hawaii and Indonesia.
Both vowed to address local issues, such as the relocation of 8,000 US Marines from Okinawa in Japan and war reparation claims.
The next major contests for the Democratic nomination take place in North Carolina and Indiana on May 6.
The two states have a combined 187 delegates at stake.
While Obama leads in nominating delegates, Clinton has moved into a virtual tie with her rival in national polls after winning in Pennsylvania last month.
Guam has been a US territory since 1898.