Services comprising setting in a wellbore a liner string including a series of zone-isolation packers and sliding sleeves, introducing pressurized fracturing fluid into the wellbore and introducing successive, sized blocking elements - drop balls - into the fracturing fluid to block the flow of fracturing fluid and open successive sliding sleeves to direct the fluid into the formation and provide multi-stage fracturing of the wellbore (terms considered too vague by the International Bureau - rule 13.2.b) of the Common Regulations)