US patents could become harder to obtain if a Supreme Court ruling into a car accelerator dispute decides to overturn a 40-year approach to deciding patent viability.

The Court heard arguments in the case yesterday, with technology giants Microsoft and Cisco supporting a change to the current rules.

The case involves a patent on "gas pedals" for vehicles, and the Supreme Court is examining how lower courts arrive at a decision that an invention was obvious, and therefore not patentable. In the case, Teleflex and Technology Holding, holders of the electronic gas pedal patent, sued KSR International for infringement, but KSR argued that the courts should invalidate the invention for obviousness.

After oral arguments yesterday, some patent lawyers said they expected the Supreme Court to overturn a four-decade-old approach to deciding obviousness - often called the teaching-suggestion-motivation test. The US Court of Appeals for the Federal Circuit has used this test, saying that there must be some proven teaching, suggestion or motivation to lead a person of ordinary skill to combine "prior art" products into a new invention for that invention to be declared obvious.

Other patent lawyers think the Supreme Court will stick with the accepted wisdom. The court last acted on the obvious standard in a 1966 ruling. One IP lawyer, Paul Andre of Perkins Coie aruged: "If the Supreme Court wanted to do it, they'd have changed it by now."

If the Supreme Court does throw out the motivation test, all current patents could be suspect, said Andre. It could mean fewer patent infringement cases brought by patent holders, because they would fear that courts would rule their patents invalid, he said. "The alleged infringer would have an easier time challenging a patent," he added.

During the session, Justices asked several questions about the obviousness standard, with Chief Justice John Roberts suggesting courts needed more flexibility to determine obviousness. The court will likely require the Federal Circuit to come up with a new standard, said Sharon Barner, an intellectual property lawyer with Foley and Lardner..

Cisco and Microsoft, joined by three other companies, filed a brief in the case saying the motivation standard makes it too hard to prove obviousness, leading to bad patents. The software giants said they had been sued for "allegedly infringing dozens of questionable patents".

The motivation test "establishes too lenient a standard for patentability, and it has had a stifling effect on true innovation because it encumbers ideas well beyond the limits imposed by Congress for patentable inventions," they argued in a brief.

But a group of patent lawyers filed a brief opposing a change in the law, saying a change in the obviousness standard could make it difficult to get a patent on any invention that combines old products. The current standard is established and well-thought, wrote lawyers for the American Intellectual Property Law Association.

Without the motivation test, there's no standard to determine obviousness, said Ronald Riley, president of the Professional Inventors Alliance, in an interview. "Things are often obvious in hindsight when they weren't that obvious."