• J.D., UCLA School of Law, 1987
  • B.A., cum laude, Claremont McKenna College, 1983


  • California, 1987
  • U.S. District Courts, Central, Northern, Eastern and Southern Districts of California
  • The U.S. Court of Appeals for the Ninth Circuit


  • California State Bar Association (sections on Litigation, Environmental Law and Real Estate Law)
  • American Bar Association (sections on Litigation and Energy, Environment and Resources)
  • Ventura County Bar Association (Natural Resources Section; previous member, Board of Directors)
  • Roberts Environmental Center, Claremont McKenna College (member of the Board of Advisors)


David Ossentjuk focuses his law practice on natural resources transactions, including asset acquisitions and dispositions, real estate conveyances, leasing, operations, title issues, joint ventures and operating agreements, carbon capture and sequestration projects, and compliance with federal, state, and local regulations. He is one of a limited number of attorneys in California with significant experience in the litigation of oil and gas disputes, including lease termination/preservation issues, unit and joint operations disputes, royalty and title matters, and post-operation environmental clean-up and abandonment issues. David also handles general business, real estate, and environmental litigation. He has successfully litigated and tried numerous business disputes involving claims for breach of contract, trespass, nuisance, fraud, breach of fiduciary duty, business interference, corporate and partnership ownership and governance, and insurance coverage.

David also has significant experience in the purchase, sale, and development of environmentally impacted properties, including the negotiation and litigation of environmental aspects of purchase and sale agreements; leases; joint ventures and partnerships; oil field development and abandonment agreements; environmental insurance policies; land use entitlements; and prospective purchaser agreements.

His professional accomplishments include:

  • Representation of the buyer in its acquisition of all of the upstream Ventura Basin assets of a major, publicly traded oil and gas company.
  • Representation of the buyer in its acquisition of upstream assets from the bankruptcy estate of an Orange County oil and gas company.
  • Successful negotiation of numerous natural resources transactions on behalf of both operators and landowners, including leases, assignments, sales, farm-ins and farm-outs, surface use agreements, licenses, rights of way and easements, seismic exploration agreements, unit and joint operating agreements, and partnership and joint venture agreements.
  • Ongoing negotiations of carbon capture and sequestration projects throughout California.
  • Prevailed in and/or resolved on favorable terms many oil and gas disputes, for both operators and landowners, on issues including lease validity and termination, royalty calculations and payments, unit and joint operations, and environmental claims and cleanups.
  • Assisted clients on numerous occasions in successfully obtaining or keeping drilling and operating permits in the context of California’s complex and evolving regulatory climate, including issues arising under the California Environmental Quality Act, the Federal Safe Drinking Water Act, and the California Public Resources Code and its implementing regulations.
  • Seven-figure jury award in the U.S. District Court in Los Angeles on a bad faith insurance claim arising from a Superfund site.
  • Favorable resolution of significant “multi-media” claims by EPA and the U.S. Justice Department against an independent refiner.
  • Trial and successful appeal of a multi-hundred-million-dollar fraud and environmental contamination judgment arising from the sale of one of the largest oil fields in the Los Angeles Basin.


  • “Oil and Gas Environmental Liability and Site Remediation in California” (2009)
  • “California Unitization of Oil/Gas Interests” (2010)
  • “Expanded DOGGR Oversight of Production Facilities” (2011)
  • “DOGGR’s Evolving View of Its Statutory Mandates and Goals and What Should We All Do in the Meantime?” (2011)
  • “Recent Changes in Division of Oil, Gas and Geothermal Resources (DOGGR) Rules and Regulations” (with Jack Quirk, Esq., 2011)
  • “Typical California Oil and Gas and Title Litigation Issues” (with John Harris, Esq., 2012)
  • “Evolving Environmental Regulation of Oil and Gas Production: ‘Fracking,’ UIC and CEQA” (2013)
  • “Oil and Gas Litigation: Selected Topics” (2013)
  • “Oil and Gas Issues in Real Estate Transactions” (2014)
  • “Legal Issues Facing the Oil and Gas Industry” (with Peter Candy, Esq. and Jack Quirk, Esq., 2015)