When very high coverage limits are required, it is often necessary for the insured to purchase two or more excess policies. This is usually because a single insurer may not have the necessary capacity to provide all of the coverage required, but also may be because the insurer does not want the entire amount of liability exposure.

 Generally, it is undesirable to have an excess liability policy directly above primary coverage. However, when the primary policy is broad enough to provide for all the insured's needs, following-form excess coverage directly above the primary policy may be acceptable. In addition, excess coverage directly above the primary policy may be necessary where primary coverage does not provide the minimum underlying limits required by the umbrella. In that case, an excess policy may be needed to fill this gap in coverage by increasing the primary limits to a level acceptable to the umbrella insurer.

 The greater the number of policies and insurers involved in an excess liability insurance program, the greater the likelihood of problems caused by inconsistent and conflicting policy terms and conditions. Excess liability policies should be, but seldom are, no less broad in coverage than the policies they follow. Subtle and unrecognized differences in language can sometimes lead to disputes and litigation over the differences in the defense and indemnity duties of insurers.