[Borek]

Take a look at the theoretical titration curves I posted earlier, especially the second one - for a weak acid/base inflection point ca be barely visible. And as the acid is weakly soluble, you are most likely dealing not with a single/simple acid/base equilibrium (which is how the theoretical curves are calculated), but with a much more complicated equilibrium, perhaps even more blurred by the kinetic effects of the acid dissolution.

[Babcock_Hall]

He already wrote it - 10 mM.

Sorry, I missed it.  "Thus, using a fluorescence-based technique [Reference 29] in 10 mM HEPES buffer (10 mM HEPES, 150 mM sodium chloride, 5 mM potassium chloride, 1 mM sodium dihydrogen phosphate, pH 7.4) at 37°C, the CMC of oleic acid was reported to be 6 μM. This is exactly consistent with our estimation of CMC using the light-scattering-based approach as shown in Fig. 2 A; all determinations are summarized in Table 3."
"29. Richieri G.V., Ogata R.T., Kleinfeld A.M. A fluorescently labeled intestinal fatty acid binding protein. Interactions with fatty acids and its use in monitoring free fatty acids. J. Biol. Chem. 1992;267:23495–23501." [PubMed]http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127186/

CMC = critical micelle concentration.  I would be concerned about what oleic acid is doing once it is formed.

[Borek]

I would be concerned about what oleic acid is doing once it is formed.

Agreed.