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Federal Circuit addresses Festo and the doctrine of equivalentsAugust 23, 2006

In a recent decision, the Federal Circuit found that a patent holder had not lost its ability to rely upon the doctrine of equivalents for its patent. The patents at issue are owned by Conoco, and relate to processes for making drag reducing agents injected into pipelines to reduce friction and therefore increase pumping efficiency.At the district court, the defendant, Energy & Environmental International (‘EEI’) stipulated that the patents were valid and enforceable, so the only issue was infringement. The case was tried to a judge, and court found EEI literally infringed one of the two patents and infringed the other under the doctrine of equivalents. The doctrine of equivalents permits patent holders to recover for infringement when a party uses a product or process that does not literally fall within the patent’s claims, but the differences are insubstantial or trivial. When a patent is amended during prosecution at the patent office, however, the patent holder often loses its right to claim infringement under the doctrine of equivalents because of prosecution history estoppel. This principle essentially bars the patent holder from claiming something infringes when he or she had narrowed the patent’s claims during prosecution from a claim that would have literally covered the allegedly infringing item to one that does not in order to obtain the patent. Here, EEI argued two grounds for prosecution history estoppel: an amendment to the claims and arguments advanced by Conoco during prosecution. The Federal Circuit rejected both arguments. First, the amendment at issue was only to correct ‘an inadvertent omission,’ caused by the cancellation of all the original claims and replacement with new claims; one limitation had been inadvertently omitted when the new claims were submitted. However, both Conoco and the patent examiner proceeded as if the limitation was still there, so the court found the amendment not to be for purposes of patentability.Second, Conoco’s arguments during prosecution did not amount to a ‘clearly and unmistakeable surrender of subject matter,’ and thus did not give rise to prosecution history estoppel. When claims are amended, there is a presumption of surrender of equivalents, but not so with arguments made to the examiner. Here, while Conoco argued ‘fatty acid wax’ did not include metal stearates, EEI’s infringing equivalent also did not contain a metal stearate. Thus, even to the extent Conoco could not claim metal stearates were equivalent, it was able to claim EEI’s fatty acid wax equivalent.This case further defines how prosecution history estoppel may arise when patents are amended during prosecution. It also highlights the differences between amendment-based estoppel and argument-based estoppel, and the differing standard for each. Statements made during prosecution of a patent can have lingering effects if the patent is ever asserted in litigation, so care must be taken to frame all official statements in the prosecution history carefully.To read the complete decision, log on to

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