Proppant Express Investments announced that on February 14, 2019 the U.S. Patent and Trademark Office invalidated 24 of 26 claims challenged by PropX from two of the four patents previously asserted by SandBox Logistics in litigation. The other two patents remain under review by the Patent Office. For the two claims not invalidated, SandBox previously dropped one from the parallel litigation against PropX. SandBox also recently conceded that PropX does not infringe the other claim based on rulings by the U.S. District Court in the Southern District of Texas. In that case, the court dismissed, with prejudice, all SandBox patent infringement claims against PropX in January 2019. SandBox is a wholly-owned subsidiary of U.S. Silica Holdings. PropX has challenged two additional SandBox patents with the Patent Office, both of which have been accepted for reexamination based on a reasonable likelihood that such patents are invalid. The Patent Office is expected to rule on the additional challenges later this year.