Julia Trigg Crawford, a farmer, plans to appeal a Lamar County judge’s ruling in favor of the oil company TransCanada.

PARIS, Tex. — The Canadian energy company TransCanada can take over land owned by a Texas farmer to build its Keystone XL pipeline, a county judge ruled on Wednesday night. In a 15-word ruling sent from his iPhone, Judge Bill Harris of Lamar County Court at Law upheld TransCanada’s condemnation of a 50-foot strip of land across Julia Trigg Crawford’s pasture here. The pipeline is being built to carry oil to Texas refineries from Canada.

Ms. Crawford plans to appeal the ruling. “We may have lost this one battle here in Paris, Texas, but we are far from done,” she said in a statement. “I will continue to proudly stand up for my own personal rights, the property rights of my family, and those of other Texans fighting to protect their land.”

The case has shed light on a loophole in Texas’s oil and gas regulation — one that critics say has given pipeline companies carte blanche to seize private land. Activists across the political spectrum have rallied behind Ms. Crawford’s cause, from conservative rural landowners and Tea Party organizations to environmental groups.

At issue was whether TransCanada is a common carrier — a company with pipeline open to any oil company willing to pay published rates. In Texas, a common carrier has the power to condemn land with little oversight.

The problem, Ms. Crawford’s supporters say, is that to earn the designation, an oil company need only claim the status itself on a one-page form submitted to the Texas Railroad Commission, which regulates pipelines.

That process has already been challenged successfully in the State Supreme Court. “No notice is given to affected parties,” Justice Don R. Willett wrote in that case, Texas Rice Land Partners v. Denbury Green. “No hearing is held, no evidence is presented, no investigation is conducted.”

In the Denbury case, the court unanimously refused the pipeline company’s condemnation claim. “Private property is constitutionally protected,” Justice Willett wrote, “and a private enterprise cannot acquire condemnation power merely by checking boxes on a one-page form.”

The court recommended a set of uniform standards for common carriers, and a body to enforce it.

But because no such body exists, Ms. Crawford’s case ended up in Judge Harris’s small courtroom. The arguments were technical. TransCanada argued that it derived its power of eminent domain from the Railroad Commission. Wendi Hammond, Ms. Crawford’s lawyer, asserted that based on a 2008 letter, the Railroad Commission said TransCanada’s operations “appear to be interstate and thereby under federal control.”

“When our own state agency says they don’t have jurisdiction,” Ms. Hammond said, “and a statute requires that a pipeline be subject to the agency’s jurisdiction, the court should be ruling in favor of the citizen and denying the corporation’s request.”

TransCanada welcomed the judge’s decision. “This ruling reaffirms that TransCanada has — and continues — to follow all state and federal laws and regulations as we move forward with the construction of the Gulf Coast Project,” said Grady Semmens, a TransCanada spokesman.In court, Ms. Hammond’s argument seemed to exasperate a TransCanada lawyer, James Freeman. He argued that under Ms. Hammond’s interpretation, “you wouldn’t be able to move interstate oil in Texas pipelines at all.”

Ms. Hammond disagreed. “We’re saying TransCanada is welcome to carry whatever they want,” she said. “They just can’t seize Ms. Crawford’s land to do it.”

Ms. Hammond was new to the case, having represented Ms. Crawford for just 11 days. Previously, Ms. Crawford’s counsel had argued that TransCanada could not be a common carrier because it carried diluted bitumen, not crude oil, because the Keystone pipeline had not yet been granted a federal permit, and because the pipeline company had not negotiated in good faith, among other things.

“That’s how this case has been all along,” Mr. Freeman said. Opposing counsel “makes these claims that have no basis in law or fact, and then by the time I get around to answering it, the argument has changed.”

Packing the courtroom were around 50 supporters of Ms. Crawford. To some, the case showed why regulatory reform was needed.

Debra Medina, a Republican former candidate for governor, said she drove seven hours to be at the hearing.

“This is a clear example of where we have a problem in our law,” Ms. Medina said, “where companies who have not proven that they are a common carrier are allowed to take property using eminent-domain — before they ever demonstrate that they meet the criteria for that use.”