A person or entity who is not a party to a lawsuit generally may intervene in the lawsuit and become a party to it by filing a plea in intervention prior to the entry of the court’s judgment—provided the court does not reject (strike) the intervention. An intervenor is not required to secure the court’s permission to intervene, and the party who opposed the intervention has the burden to challenge it by filing a motion to strike.

A person or entity has a right to intervene if the intervenor could have brought the same lawsuit, or any part of it in his own name—or, if the action had been brought against him, he would be able to defeat the lawsuit, or some part of it.

A trial court abuses its discretion by striking an intervention if (1) the intervenor meets the above test, (2) the intervention will not complicate the case by an excessive multiplication of the issues, and (3) the intervention is almost essential to effectively protect the intervenor’s interest.

In Oklahoma, a person or entity not originally part of a lawsuit can intervene in the case by filing a plea in intervention before the court's judgment is entered. This is allowed as long as the intervention is not struck by the court. The intervenor does not need to obtain permission from the court to intervene, but if the intervention is opposed, the opposing party must file a motion to strike to challenge it. An entity has the right to intervene if they could have initiated the same lawsuit on their own, or if they could defend against the lawsuit or a portion of it. A trial court in Oklahoma may be found to have abused its discretion if it strikes an intervention when the intervenor meets the criteria of being able to bring or defend against the lawsuit, the intervention does not excessively complicate the case, and the intervention is nearly essential to protect the intervenor's interests.