Scotland had a history of full-scale shale oil production from 1850-1962 and was a key developer of many of the technologies still used in modern-day, above ground retorting processes. The central Scotland oil shale field is only a tenth the size of the Estonian oil shale field (194 km(2)) with 7 main oil bearing seams. Remaining resources are calculated at 1,100 million tonnes. The Scottish shale-oil industry mainly produced oil for petrol, lighting and lubricating. In addition extensive use was made of the waste products, like ammonia, that were created in retorting process. The spent shale was typically about 75% of the weight of the raw shale and was tipped onto shale bings (spoil heaps) up to 95 metres high; much of this spoil was also utilised in a range of by-products.