A friend of mine has been advocating "magnesium oil" as an alternative to oral magnesium supplements. Products based on this are widely advertised and promoted on the web.
But in this Skeptics Stack Exchange discussion Does an Epsom salt bath provide relief from muscular pain? sources are cited saying that magnesium is not efficiently absorbed trandermally, e.g., http://journals.sagepub.com/doi/pdf/10.1177/1535370214537745, but unfortunately Sage is behind a paywall so I can't access the full-text article.
On the other side of the argument is this article in Nutrition Practitioner by Watkins and Josling http://www.cnelm.com/NutritionPractitioner/Issues/Issue_11_1/Articles/7%20Transdermal%20Mg%20revised2.pdf claiming in their small study to demonstrate efficient absorption of magnesium transdermally.
An important difference between the Epsom salt question and the "magnesium oil" claims is the role (if any) of being in a lipid suspension (or is it a solution - I have no idea what "magnesium oil" is.)
So does the presence of the oil somehow make it possible to absorb magnesium though the skin, in a way that a magnesium salt in an aqueous solution wouldn't, or is the Watkins and Josling article Bad Science?