In a contested divorce, the parties have been unable to resolve their differences on one or more terms of the divorce such as child custody or property division, which remain highly disputed and may result in divorce litigation. When the spouses cannot agree on an issue, or issues in the case, a spouse files a petition requesting the court to terminate the marriage and resolve any issue which is contested. Once a response is filed, the discovery phase of litigation begins. Each spouse answers questions under oath in writing, or orally at a deposition. In certain contested cases, witnesses may be identified and experts may be hired when necessary. A contested divorce is often far more costly than a case where the parties can resolve all issues by agreement.