Last January, Geoffrey Smith, a scholar of early Christianity at the University of Texas, noticed something startling: an eBay listing for an ancient Greek papyrus fragment of the Gospel of John — with an opening bid of only $99.

“I thought, This can’t be allowed to sell on eBay,” Dr. Smith said. “It will just disappear into a private collection.”

Dr. Smith contacted the seller and urged him to halt the online auction — apparently the first on eBay for a Greek New Testament papyrus, he and other scholars said — and let him study the fragment. The seller agreed, and now, on Saturday, Mr. Smith will present his research at the annual conference of the Society of Biblical Literature in Atlanta.

The credit-card-size papyrus, which Dr. Smith dates from around A.D. 250 to A.D. 350, contains about six lines of the Gospel of John on one side and an unidentified Christian text on the other. If Dr. Smith’s analysis is correct, it is the only known Greek New Testament papyrus from an unused scroll rather than a codex, the emerging book technology that early Christians, in sharp contrast to their Jewish and pagan contemporaries, preferred for their texts.