Research · October 2026
We pulled the assignment record for 500 randomly sampled US utility patents granted in 2020 and checked each one the way a buyer or lender would. About one in 15 still carries an unreleased lien, and one in 7 has already expired for unpaid fees.
7%
still carry an unreleased lien
A security interest is recorded against the patent and no release is on record. Some of these loans are still outstanding; others were repaid and the release was never filed. Either way, a buyer or new lender has to clear it.
34 of 500 patents
14%
have an inventor with no recorded assignment
At least one named inventor never appears as an assignor in the record. Patents owned by their own inventor are excluded. The assignment may exist and simply never have been recorded, but the record alone does not show the owner received that inventor’s rights.
68 of 500 patents
13%
have an assignment recorded more than three months after it was signed
Under 35 U.S.C. 261, an assignment recorded within three months is protected against a later buyer of the same patent. Recording later leaves a window in which a second sale could take priority.
65 of 500 patents
14%
have already expired for unpaid maintenance fees
The USPTO status shows the patent expired because a maintenance fee was not paid. For patents granted in 2020 that is the first fee, due 3.5 years after grant. An expired patent can no longer be enforced, although it is only about six years old.
68 of 500 patents
11%
are now recorded under a different owner than the original applicant
A sale, merger, or name change moved the patent away from the name it was filed under. Each one is another link a buyer has to verify.
56 of 500 patents
8%
are co-owned by two or more parties
Under US law each co-owner can generally use and license the patent without the others’ consent, and all co-owners usually have to join to sue. Co-ownership is often intended, but it limits what any one owner can sell or enforce.
38 of 500 patents
Entity size is the fee status claimed with the USPTO; small and micro entities are mostly individual inventors, startups, small companies, universities, and nonprofits. Smaller groups have wider margins of error, so treat differences of a few points as noise.
| Group | Patents | Unreleased lien | Inventor not on record | Recorded > 3 months late | Expired, unpaid fees | New owner of record | Co-owned |
|---|---|---|---|---|---|---|---|
| All patents | 500 | 7% | 14% | 13% | 14% | 11% | 8% |
| US inventors only | 234 | 11% | 16% | 18% | 14% | 12% | 8% |
| Any non-US inventor | 266 | 3% | 11% | 8% | 14% | 10% | 8% |
| Small or micro entity | 111 | 5% | 28% | 17% | 16% | 10% | 10% |
| Large entity | 389 | 7% | 10% | 12% | 13% | 12% | 7% |
None of these findings is rare. Across 50 patents picked at random, these rates mean about 3 with an unreleased lien, 7 with an inventor missing from the record, and 7 already lapsed. Within one company’s portfolio they tend to cluster instead: a single unreleased loan usually covers every patent the company pledged. Most will turn out to have an explanation, but each one has to be found and resolved before the patent can be sold, pledged, or asserted with confidence.
Finding them means reading every recorded conveyance for every patent. That is the step that takes a paralegal days on a mid-sized portfolio, and it is what the free patent ownership check and the full Patencial report automate. See also the patent purchase due diligence checklist and patent collateral diligence for lenders.
These are findings about the public record, not legal conclusions about title. Records can be incomplete, and name matching across records is automated, so individual results should be confirmed against the underlying documents.
We drew 500 patents at random from the 351,968 US utility patents granted in 2020, using the USPTO Open Data Portal. Every patent granted that year had the same chance of being picked. The random seed is published so the sample can be reproduced.
Patents granted around five years ago have had time to be sold, pledged as collateral, and reach their first maintenance fee deadlines, so the record reflects a realistic life cycle. Very recent grants would undercount transfers and liens.
No. It means a security interest was recorded and no release was recorded afterwards. Many of these loans were repaid, and the lender simply never recorded a release. The record still shows the patent as pledged until someone records one.
Not necessarily. The assignment may have been signed but never recorded, or the inventor may have been obligated to assign under an employment agreement. Since the America Invents Act let companies file as the applicant, unrecorded inventor assignments are common. The point is that the public record alone does not prove the transfer.
Yes. The free patent ownership check runs the same checks used in this study on any single US patent.
Free patent ownership check
Enter a US patent number to see the owner of record, every recorded assignment, and anything a buyer would want explained.
Read guidePatent chain of title verification
Reconstruct ownership from the named inventors to the current assignee, with every defect cited to a USPTO record.
Read guide35 U.S.C. 261: patent assignments and recording
What Section 261 requires for a valid assignment, and why the three-month recording window decides priority.
Read guidePost-AIA chain of title gaps
How assignee filing under the America Invents Act can leave an inventor assignment unrecorded, and how to find the gap.
Read guidePatent security interests and liens
How a pledged patent shows up in the USPTO record, why an unreleased lien blocks a clean transfer, and what lenders check.
Read guideHow to buy a patent
The patent purchase process start to finish, with the due diligence checklist buyers run before closing.
Read guidePatent due diligence for M&A
What patent diligence checks before a deal closes, starting with clean ownership of every patent.
Read guideUpload patent numbers. Get a source-cited report in minutes. No credit card required.