The common interest doctrine sometimes allows separately represented clients to avoid the normal privilege waiver implications when sharing their privileged communications. Unfortunately for lawyers hoping for certainty, states and even courts within the same state disagree about the prerequisites for such contractual non-waiver protection.

In Luckenbach Texas, Inc. v. Engel, the court pointed to Fifth Circuit law finding the common interest doctrine available if there is a "palpable threat of litigation at the time of the communication, rather than a mere awareness" of possible litigation. No. 1:19-CV-00567-DH, 2022 U.S. Dist. LEXIS 187911, at *7-8 & *10-11 (W.D. Tex. Oct. 14, 2022) (citation omitted). But the court also held that the common interest doctrine "turns not on whether the parties are potential or actual co-defendants" – or "whether the parties are sued in the same lawsuit or not." Id. at *8-9. Somewhat surprisingly, the Texas federal court did not even mention a Texas state court rule that seems to limit the common interest doctrine protection to parties in actual ongoing litigation. Texas R. Evid. Rule 503(b)(1) (limiting the privilege to participants "in a pending action").

Such stark differences in courts even within the same state highlight the uncertain application of the common interest doctrine protection.