There is no such thing as sustainable palm oil: Palm oil: the hidden ingredient causing an ecological disaster
Less than 7% of total palm production is currently certified as sustainable. Furthermore manufacturers are proving reluctant to pay the premium associated with this product.
Manufacturers may claim to be using sustainable palm oil because they are members of, or supplied by members of, the Roundtable on Sustainable Palm Oil. However, this in itself is no guarantee as members only need commit to "working towards" producing a sustainable product.