Ourg bones are used to train the Prayer skill. When buried, they give 140 Prayer experience.
Ourg bones can be obtained by either stealing them from Ogre coffins via the Thieving skill or using keys dropped by Zogres and Skogres on nearby chests. They are also a possible loot from Zombie Implings and can also be dropped by General Graardor. Although General Graardor's bones look different, and are treated as a completely different item on the Grand Exchange, they still give the same amount of experience when buried. Ourg bones give the second highest amount of Prayer experience of any re-obtainable bone, following frost dragon bones.
While training, multiple dragon bones can be bought for the price of one Ourg bone. Just two dragon bones gives 144 experience, which is 4 more experience than a single Ourg bone. If inventory space is an issue, Ourg bones may be a more suitable choice, especially if using on a house altar or the Ectofuntus.
They give 490 prayer experience when used on a gilded altar with both incense burners lit, and 560 prayer experience when used with the Ectofuntus. It is advised to sell Ourg Bones that you get from an Ogre Coffin rather than using them because of their high price/experience.
In the FunOrb game Armies of Gielinor, there is a Bandos unit available called "Ourg" with an image extremely similar to Graardor. When Armies of Gielinor was first released, it was unconfirmed that Graardor was actually Ourg, however it has since been confirmed in Postbag from the Hedge 39 and with the addition of Ourg bones to Graardor's drops.