California has adopted the "cause" approach for determining the number of occurrences.  State Farm Fire and Cas. Co. v. Kohl, 131 Cal. App.3d 1031 (1982).  See also Meade Reinsurance v. Granite State Ins. Co., 865 F.2d 992 (9th Cir. 1988).  Cf. Bay Cities Paving & Grading, Inc. v. Lawyer's Mut. Ins. Co., 5 Cal. 4th 854, 855 P.2d 1263 (1993)(distinguishing rule for "claims made" policies).
 
As yet, few California courts have not been called upon to determine the number of "occurrences" in pollution or mass tort cases.  In the Coordinated Asbestos Cases, Judge Brown ruled cases that each personal injury claimant was a separate "occurrence," rejecting insurers' arguments that claims should be aggregated by type of product, location of exposure or other common conditions.  These cases have come to conflicting conclusions.  Compare State Farm Fire & Cas. Co. v. Elisabeth N.,  9 Cal. App. 4th 1232, 12 Cal. Rptr.2d 327 (1st Dist. 1992)(multiple instances of child molestation at insured day care facility all arose out of "exposure to the same general conditions (insured's negligence in failing to provide adequate care and supervision for children) and therefore constitute only one "occurrence"); Vandenberghe v. Amco Ins. Co., 1992 U.S. Dist. LEXIS 10760 (N.D. Cal. July 10, 1992)(homeowners' claims against plumber for negligent pipe insulation involved diverse "occurrences", notwithstanding fact that work was all performed pursuant to one contract, where different physical factors caused each claimant's loss) with Chemstar, Inc. v. Liberty Mut. Ins. Co., 797 F.Supp. 1541 (C.D. Cal. 1992), aff'd, 41 F.3d 429 (9th Cir. 1994) (contractor's failure to warn homeowners that plaster product was unsuitable for use was "cause" of all ensuing claims involving unsightly blemishes to their homes).

Judge Bea ruled in Tosco Corp.  v.  Hartford Accident & Indemnity Co., San Francisco No.  952681 (Cal.  Super.  March 1, 1999) that a “cause” approach should be used for pollution claims and declared that policies containing a “deemer” clause which or which provide that damage resulting from “continuous or repeated exposure to substantially the same conditions existing at or emanating from one premises location” will be treated as a single occurrence for each site.

The Court of Appeal has also ruled that a scheme by which various trucking companies allegedly stole $1.5 million in petroleum products in 650 separate incidents constituted only a single "occurrence" for the purpose of determining the available "fidelity" coverage rather than multiple "occurrences" as its property insurer had contended. Eott Energy Corp. v. Store Brand International Ins. Co., 45 Cal.App.4th 565, 52 Cal.Rptr.2d 894 (2d Dist.  1995).  But see B.H.D., Inc. v. Nippon Ins. Co. of Europe, Ltd, 54 Cal. Rptr.2d 272 (Cal. App.  1996)(A $10,000 deductible for "each claim for loss or damage (separately occurring)" held to apply separately to each of numerous incidents in which a customer stole jewelry from the insured's store over a period of months).

Where a continuing loss arising out of a single “occurrence” triggers multiple policy limits, a federal district court has ruled that an insured is not entitled to “stack” the separate occurrence limits in the subject policies.  Employers Insurance of Wausau v. Granite State Insurance Company, No. CV 92-0406 (C.D. Cal. March 14, 2001)(land subsidence).  The court refused to find that th policy limit should be interpreted as “per occurrence per year.”