Mary Ann Joerres received her undergraduate degree, summa cum laude, in 1981 from Marquette University, where she was elected to Phi Beta Kappa, and she received her law degree, summa cum laude, from Marquette University Law School in 1985.

Mary Ann started the practice of law as an associate at Lord, Bissell & Brook in Chicago, Illinois, where she worked in the antitrust and securities litigation department. Mary Ann moved to Dallas and joined Hughes & Luce in 1986. Mary Ann practiced as an associate at Hughes & Luce from June of 1986 until December of 1992. She became a partner in 1993 and remained in that position until she joined Diamond McCarthy in March of 2001.

Mary Ann has worked on a variety of civil litigation matters, including lender liability as well as other disputes involving financial institutions, securities fraud, antitrust, engineering malpractice, toxic torts, products liability, oil and gas and ERISA. Cases in which Mary Ann has been involved as the lead litigator have included:

• The defense of a large oil producing company in a number of related proposed class action cases involving the propriety of royalty payments for crude oil production and the use of posted prices in connection therewith. Plaintiffs brought the cases on behalf of classes of royalty owners (varying in geographic scope). For purposes of effectuating a global (nation-wide) settlement, defendants agreed to consolidate this group of cases into a Multi-District Litigation proceeding in federal court with another series of similar cases.
• The defense of a large gas producing company in a number of proposed class action cases involving the propriety of royalty payments for gas and natural gas liquids production. The Plaintiffs' claims focused on affiliate sales and the pricing structure of such sales.
• The defense of a large oil producing company in an action brought under the False Claims Act, 31 U.S.C. 3729, et seq. in the United States District Court for the Eastern District of Texas. The case was originally filed by private relators on behalf of the United States under the qui tam provisions of the False Claims Act. The Plaintiffs alleged that the defendant oil companies had engaged in numerous schemes, and had filed hundreds of thousands of false reports with the Department of Interior, with the intent to underpay royalties on crude oil extracted from federal and Indian lands.
• The prosecution of a class action suit on behalf of a class of employees (and their beneficiaries) of a large corporation in the defense industry, claiming breaches of ERISA, fiduciary duties and other applicable laws in connection with their multi-part pension plan. A class and subclass was certified. The case was settled and the settlement approved by the Court at the final fairness hearing.
• Defense of a major bank holding company in a series of multi-million dollar lawsuits involving the correspondent lending relationship between the client's subsidiary banks and other non-affiliated banks and the non-affiliated bank's issuance of commercial paper. The claims included RICO, alleged securities law violations and antitrust violations and other lender liability theories.
• Defense of the second largest gas producer in the state of Michigan in a proposed class action involving the propriety of royalty payments for gas and natural gas liquids production. The Plaintiffs' claims focus on affiliate sales, the pricing of such sales, and the deductions taken therefrom in the calculation of royalty payments. The case is pending.

Other cases in which Mary Ann has been involved as a participating member of a trial team have included:

• Representing of the country's leading life insurance companies and lenders to the hotel industry in a multi-million dollar case brought against it by one of its borrowers on claims of lender liability, alleged antitrust violations and unfair competition.
• Defending environmental claims against a company that had recently purchased several gas processing plants. A neighboring landowner of one of the plants filed trespass, nuisance, and personal injury claims relating to operations both before and after the acquisition.
• Representing an international civil/environmental engineering firm against a multi-million dollar claim for professional malpractice regarding the design, and management of construction, of a large wastewater treatment plant.
• Defending a manufacturer of cadmium and nickel batteries in a toxic tort case.
• Defending an international financial company, a national mortgage company and other defendants in a case brought on behalf of a hotel developer and various companies in which he and his partners had an interest. Plaintiffs alleged that defendants improperly declared a default under the loan agreements and refused to deal with plaintiffs in good faith. Plaintiffs' claims included breach of contract, fraud, and tortious interference with contract.

Mary Ann is a member of the State Bars of Texas, Illinois and Wisconsin, the American Bar Association, and the Dallas Bar Association. She is admitted to practice before the United States District Courts for the Northern, Southern, Eastern, and Western Districts of Texas, the United States District Courts for the Northern and Western Districts of Oklahoma as well as the United States Court of Appeals for the Fifth Circuit.

Mary Ann has spoken on a variety of topics, including class actions and disputes involving mineral interests and royalty payments to the Southwestern Legal Foundation, the Energy Section of the Dallas Bar Association, the American Association of Professional Landmen and the Dallas Association of Petroleum Landmen.