All HQi tanks are bunded. This means that the tank is double skinned and can hold 110% of the inner tank's capacity in order to protect your valuable heating oil in the event of the inner tank splitting. Single skin tanks will not offer protection against tank splits. That's why Harlequin urges homeowners to 'Buy Safe, Buy Bunded'. Harlequin HQi bunded oil tanks have been designed for customers who do not require the additional technological benefits as featured on all Harlequin 'iTank' oil storage tanks. HQi bunded oil tanks offer a 'no nonsense' oil storage solution and are available in 11 different tank capacities, ranging from 350 litres, to 3,500 litres.