OXFORD, Pennsylvania — There are many people with theories about what happened to Amelia Earhart. But few stir up more excitement – or more ire – than Ric Gillespie.

The longstanding official theory is that the famed pilot and her navigator, Fred Noonan, ran out of gas and crashed into deep ocean waters northwest of Howland Island, a tiny speck in the South Pacific that the pair missed while attempting a round-the-world flight in 1937.

Since 1989, Gillespie and The International Group for Historic Aircraft Recovery, or TIGHAR, have been testing another theory – and they’ve headed back to the region this month. They surmise that Earhart made an emergency landing on a flat stretch of coral reef off that was then known as Gardner Island, southwest of Howland. And they’ve raised millions in private funds to finance several treks to the distant atoll, now called Nikumaroro.

Set to arrive this weekend, the TIGHAR team now wants to check an anomaly seen in sonar imaging on an underwater cliff where the reef drops off.

Could it be the fuselage of Earhart’s Lockheed Electra 10E airplane?

Gillespie makes no promises: “There’s no guarantee of success.”

He’s far from the only one looking for Earhart.

An Australian researcher thinks wreckage spotted by members of his country’s military years ago on a Papua New Guinea island could be hers. Others are investigating local lore that Earhart and Noonan crash landed on Mili Atoll, 800 miles northwest of Howland, and died in Japanese hands.

Various teams who believe the crashed-and-sank theory – an explanation supported by curators at the Smithsonian’s Air and Space Museum – have tried to find the plane using sophisticated equipment to scan the ocean floor. No one has found a verified plane part or bone fragment.

But Gillespie says he and his team are building their case, slowly but surely.

He has his admirers. In 2012, then Secretary of State Hillary Clinton recognized Gillespie at a reception honoring Earhart.

But there’ve been disappointments and controversy, too.There was the filing cabinet discovered on Nikumaroro that the team thought came from Earhart’s plane but later linked to a military aircraft. The team also excavated a grave that turned up bones, not of the famous pilot but of a tiny infant.

One of TIGHAR’s more controversial finds is a piece of metal, likely from an airplane, which the team found at Nikumaroro in the early 1990s. Gillespie’s latest theory is that it’s a patch that covered a window on Earhart’s plane. Many critics dispute that, though Gillespie has at least one notable supporter – MIT engineering professor Thomas Eagar who thinks it may be “the real thing.”

Over the years, Gillespie and his team have found other items in what they think is an old castaway camp. These, they say, aren’t as easily explained – heel fragments from a woman’s shoe, a rusted jack- knife and fragments of toiletries they believe are from the 1930s. Their own expert’s high-tech analysis of an object in an old photograph of the island determined that it could be Lockheed landing gear jutting from the reef before being washed away, they say.

None of it is definitive proof, he and his team realize.

“We have compiled a preponderance of evidence suggesting – not proving – that our hypothesis is true,” says Tom King, TIGHAR’s lead archaeologist.

Some critics insist that Gillespie has found nothing remotely tied to Earhart. Then there’s Tim Mellon, a one-time supporter and now critic, who thinks quite the opposite – that Gillespie knows more than he reveals. Two years ago, Mellon accused Gillespie in an unsuccessful lawsuit of hiding the fact that he’d found Earhart’s plane so Mellon would donate more than $1 million in stock to help fund the 2012 expedition.

Meanwhile, Gillespie says, “Amelia inspires passion. I understand that. But my skin got thick a long time ago.”

And so the 68-year-old pilot with a background in airplane accident investigation continues his search.