HBP is 'held by production. When you sign a lease, it will have a primary term (most commonly 3 years) which is the time that the lessee can plan or otherwise be inactive. At the end of the primary term, the lease will continue if there is a producing well or the lessee is drilling a well, depending on the exact lease terms. Then the lease continues as long as there is production. There are many 1950's leases which are still HBP. DPU is a Declaration of Pooled Unit or Declaration of Pooled Unit. It is the document which declares that separate leases and tracts of acres are combined for drilling a horizontal well (in your case). A horizontal well needs a long strip of acres. Suppose there are 4 tracts of 40 acres each and it takes 160 acres to drill. Then the oil company needs to set out that it has authority to pool the tracts and how the oil will be allocated to the tracts and owners. Most commonly, allocated on a per acre basis. That is the DPU. You want to make sure that your minerals/acres are not left out and isolated so they can never be drilled and you want the best financial deal possible. Finally, if your minerals are already pooled, then the operator may want to drill across one or more pooled units. In that case, the document will be a PSA, Production Sharing Agreement, which will describe the terms and conditions of drilling the horizontal well across the units and sharing the production between the units, most commonly by length of lateral in each unit.