pre-compliance purposes are doing so with the expectation, or as a hedge against the possibility, of future mandatory cap and trade regulations. As a mandatory cap would sharply increase the price of offsets, firms—especially those with large carbon footprints and the corresponding financial exposure to regulation—make the decision to acquire offsets in advance at what are expected to be lower prices. Retail Multiple players in the retail market have offerings that enable consumers and businesses to calculate their carbon footprint, most commonly through a web-based interface including a calculator or questionnaire, and sell them offsets in the amount of that footprint. In addition many companies selling products and services, especially carbon-intensive ones such as airline travel, offer options to bundle a proportional offsetting amount of carbon credits with each transaction. Suppliers of voluntary offsets operate under both nonprofit and social enterprise models, or a blended approach sometimes referred to as triple bottom line. Other suppliers include broader environmentally focused organizations with website subsections or initiatives that enable retail voluntary offset purchases by members, and government created projects. Features of companies that voluntarily offset emissions Companies that voluntarily offset their own emissions tend to be of relatively low carbon intensity, as they can offset a significant proportion of their emissions at relatively low cost. Voluntary offsetting is particularly common in the financial sector. 61 per cent of financial companies in the FTSE 100 offset at least a portion of their 2009 emissions. Twenty-two per cent of financial companies in the FTSE 100 considered their entire 2009 operations to be carbon neutral. In 2015, the UNFCCC created a dedicated website where organizations and companies as well as private persons are able to offset their footprint with the aim of facilitating everyone's participation in the process of promoting sustainability on a voluntary basis. Types of offset projects The CDM identifies over 200 types of projects suitable for generating carbon offsets, which are grouped into broad categories. These project types include renewable energy, methane abatement, energy efficiency, reforestation and fuel switching (i.e. to carbon-neutral fuels and carbon-negative fuels). Renewable energy It is hard to show additionality for these projects. Methane collection and combustion Some offset projects consist of the combustion or containment of methane generated by farm animals (by use of an anaerobic digester), landfills or other industrial waste. Methane has a global warming potential (GWP) 23 times that of CO2. When combusted, each