U.S. Patent No. 8,171,993, directed to heated water flow for fracing.
61 frac jobs, worth $1.8 million, were performed by Patentee prior to the critical date even though the Patentee new of the timing of the patient process (page 5). The 61 prior jobs were not disclosed to the Patent Office (page 5). The PTO issued a continuation with different claims after disclosure of the 61 prior jobs (page 10). The 61 frac jobs were not experimental as there were payments, no notes were kept about the claimed use, and any improvements were not directed to the claimed invention (pages 11-12). Since the claims of the continuation are materially different and are directed to the improvements of the alleged experimentation, the issuance of the continuation claims over the 61 frac jobs does not make the 61 frac jobs not material (page 13).
Hindsight: It may be best to explore all possible bars when drafting and to disclose any possible bars to the PTO. Relating the claims directly to any experimentation and taking notes on the experimentation (among other things) may avoid prior use. For the continuation case, prosecuting the identical claims or with very minor variation to allowance over the 61 frac jobs but not necessarily over statutory double patenting may better show that the 61 frac jobs were not material.